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Network Working Group                                           M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                              D. Balfanz
Expires: July 8, 2011                                             Google
                                                              J. Bradley
                                                             independent
                                                               Y. Goland
                                                               Microsoft
                                                               J. Panzer
                                                                  Google
                                                             N. Sakimura
                                               Nomura Research Institute
                                                               P. Tarjan
                                                                Facebook
                                                        January 04, 2011


               JSON Web Token (JWT) - Claims and Signing
                     draft-jones-json-web-token-01

Abstract

   JSON Web Token (JWT) is a means of representing signed content using
   JSON data structures, including claims to be transferred between two
   parties.  The claims in a JWT are encoded as a JSON object that is
   digitally signed and optionally encrypted.  Encryption for JWTs is
   described in a separate companion specification.

   The suggested pronunciation of JWT is the same as the English word
   "jot".

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months



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   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 8, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  JSON Web Token (JWT) Overview  . . . . . . . . . . . . . . . .  7
     3.1.  Example JWT  . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  JWT Claims . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Reserved Claim Names . . . . . . . . . . . . . . . . . . .  8
     4.2.  Public Claim Names . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Private Claim Names  . . . . . . . . . . . . . . . . . . . 11
   5.  JWT Header . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Reserved Header Parameter Names  . . . . . . . . . . . . . 11
     5.2.  Public Header Parameter Names  . . . . . . . . . . . . . . 13
     5.3.  Private Header Parameter Names . . . . . . . . . . . . . . 13
   6.  Rules for Creating and Validating a JWT  . . . . . . . . . . . 13
   7.  Base64url encoding as used by JWTs . . . . . . . . . . . . . . 17
   8.  Signing JWTs with Cryptographic Algorithms . . . . . . . . . . 17
     8.1.  Signing a JWT with HMAC SHA-256  . . . . . . . . . . . . . 18
     8.2.  Signing a JWT with RSA SHA-256 . . . . . . . . . . . . . . 19
     8.3.  Signing a JWT with ECDSA P-256 SHA-256 . . . . . . . . . . 20
     8.4.  Additional Algorithms  . . . . . . . . . . . . . . . . . . 21
   9.  JWT Serialization Formats  . . . . . . . . . . . . . . . . . . 21
     9.1.  JWT Compact Serialization  . . . . . . . . . . . . . . . . 21
     9.2.  JWT JSON Serialization . . . . . . . . . . . . . . . . . . 22
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 23
     11.1. Unicode Comparison Security Issues . . . . . . . . . . . . 23
   12. Open Issues and Things To Be Done (TBD)  . . . . . . . . . . . 24
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     13.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  JWT Examples  . . . . . . . . . . . . . . . . . . . . 27
     A.1.  JWT using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 27
       A.1.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 28
       A.1.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 29
       A.1.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 30
     A.2.  JWT using RSA SHA-256  . . . . . . . . . . . . . . . . . . 30
       A.2.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 30
       A.2.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 34
       A.2.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 35
     A.3.  JWT using ECDSA P-256 SHA-256  . . . . . . . . . . . . . . 35
       A.3.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 35
       A.3.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 37
       A.3.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 37
     A.4.  JWT using JSON Serialization . . . . . . . . . . . . . . . 38
       A.4.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 38
       A.4.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 39
       A.4.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 39



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   Appendix B.  Notes on implementing base64url encoding without
                padding . . . . . . . . . . . . . . . . . . . . . . . 39
   Appendix C.  Relationship of JWTs to SAML Tokens . . . . . . . . . 40
   Appendix D.  Relationship of JWTs to Simple Web Tokens (SWTs)  . . 41
   Appendix E.  Acknowledgements  . . . . . . . . . . . . . . . . . . 41
   Appendix F.  Document History  . . . . . . . . . . . . . . . . . . 41
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42












































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1.  Introduction

   JSON Web Token (JWT) is a compact token format intended for space
   constrained environments such as HTTP Authorization headers and URI
   query parameters.  JWTs encode claims to be transmitted as a JSON
   object (as defined in RFC 4627 [RFC4627]) that is base64url encoded
   and digitally signed.  The JWT signature mechanisms are independent
   of the type of content being signed, allowing arbitrary content to be
   signed.  Encryption for JWTs is described in a separate companion
   specification.

   The suggested pronunciation of JWT is the same as the English word
   "jot".


2.  Terminology

   JSON Web Token (JWT)  A data structure containing three JWT Token
      Segments: the JWT Header Segment, the JWT Payload Segment, and the
      JWT Crypto Segment.  The JWT Payload Segment typically represents
      a set of claims convened by the JWT as a JSON object, but in the
      general case, may represent arbitrary signed content.

   JWT Compact Serialization  A data structure representing a JWT as a
      string consisting of three JWT Token Segments: the JWT Header
      Segment, the JWT Payload Segment, and the JWT Crypto Segment, in
      that order, with the segments being separated by period ('.')
      characters.

   JWT JSON Serialization  A data structure representing a JWT as a JSON
      object with members for each of three kinds of JWT Token Segments:
      a "header" member whose value is a non-empty array of JWT Header
      Segments, a "payload" member whose value is the JWT Payload
      Segment, and a "signature" member whose value is a non-empty array
      of JWT Crypto Segments, where the cardinality of both arrays is
      the same.

   JWT Token Segment  One of the three parts that make up a JSON Web
      Token (JWT).  JWT Token Segments are always base64url encoded
      values.

   JWT Header Segment  A JWT Token Segment containing a base64url
      encoded JSON object that describes the signature applied to the
      JWT Header Segment and the JWT Payload Segment.







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   JWT Payload Segment  A JWT Token Segment containing base64url encoded
      content.  This may be a JWT Claims Object.

   JWT Crypto Segment  A JWT Token Segment containing base64url encoded
      cryptographic signature material that secures the JWT Header
      Segment's and the JWT Payload Segment's contents.

   Decoded JWT Header Segment  A JWT Header Segment that has been
      base64url decoded back into a JSON object.

   Decoded JWT Payload Segment  A JWT Payload Segment that has been
      base64url decoded.  If the corresponding JWT Payload Segment is a
      JWT Claims Object, this will be a Decoded JWT Claims Object.

   Decoded JWT Crypto Segment  A JWT Crypto Segment that has been
      base64url decoded back into cryptographic material.

   JWT Claims Object  A base64url encoded JSON object that represents
      the claims contained in the JWT.

   Decoded JWT Claims Object  A JSON object that represents the claims
      contained in the JWT.

   JWT Signing Input  The concatenation of the JWT Header Segment, a
      period ('.') character, and the JWT Payload Segment.

   Digital Signature  For the purposes of this specification, we use
      this term to encompass both Hash-based Message Authentication
      Codes (HMACs), which can provide authenticity but not non-
      repudiation, and digital signatures using public key algorithms,
      which can provide both.  Readers should be aware of this
      distinction, despite the decision to use a single term for both
      concepts to improve readability of the specification.

   Base64url Encoding  For the purposes of this specification, this term
      always refers to the he URL- and filename-safe Base64 encoding
      described in RFC 4648 [RFC4648], Section 5, with the '=' padding
      characters omitted, as permitted by Section 3.2; see Section 7 for
      more details.

   Header Parameter Names  The names of the members within the JSON
      object represented in a JWT Header Segment.

   Header Parameter Values  The values of the members within the JSON
      object represented in a JWT Header Segment.






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   Claim Names  The names of the members of the JSON object represented
      in a JWT Claims Object.

   Claim Values  The values of the members of the JSON object
      represented in a JWT Claims Object.


3.  JSON Web Token (JWT) Overview

   JWTs represent content that is base64url encoded and digitally
   signed, and optionally encrypted, using JSON data structures; this
   content is typically a set of claims represented as a JSON object.

   When the JWT payload is a set of claims, the claims are represented
   as name/value pairs that are members of a JSON object.  The JSON
   object is base64url encoded to produce the JWT Claims Object, which
   is used as the JWT Payload Segment.  An accompanying base64url
   encoded JSON header - the JWT Header Segment - describes the
   signature method used.

   The names within the header object MUST be unique.  The names within
   the header object are referred to as Header Parameter Names.  The
   corresponding values are referred to as Header Parameter Values.
   Likewise, if the payload represents a JWT Claims Object, the names
   within the claims object MUST be unique.  The names within the claims
   object are referred to as Claim Names.  The corresponding values are
   referred to as Claim Values.

   JWTs contain a signature that ensures the integrity of the content of
   the JWT Header Segment and the JWT Payload Segment.  This signature
   value is carried in the JWT Crypto Segment.  The JSON Header object
   MUST contain an "alg" parameter, the value of which is a string that
   unambiguously identifies the algorithm used to sign the JWT Header
   Segment and the JWT Payload Segment to produce the JWT Crypto
   Segment.

3.1.  Example JWT

   The following is an example of a JSON object that can be encoded to
   produce a JWT Claims Object:
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Base64url encoding the UTF-8 representation of the JSON object yields
   this JWT Claims Object, which is used as the JWT Payload Segment:
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ




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   The following example JSON header object declares that the encoded
   object is a JSON Web Token (JWT) and the JWT Header Segment and the
   JWT Payload Segment are signed using the HMAC SHA-256 algorithm:
   {"typ":"JWT",
    "alg":"HS256"}

   Base64url encoding the UTF-8 representation of the JSON header object
   yields this JWT Header Segment value:
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

   Signing the UTF-8 representation of the JWT Signing Input (the
   concatenation of the JWT Header Segment, a period ('.') character,
   and the JWT Payload Segment) with the HMAC SHA-256 algorithm and
   base64url encoding the result, as per Section 8.1, yields this JWT
   Crypto Segment value:
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

   Concatenating these segments in the order Header.Payload.Signature
   with period characters between the segments yields this complete JWT
   using the JWT Compact Serialization (with line breaks for display
   purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

   This computation is illustrated in more detail in Appendix A.1.


4.  JWT Claims

   If the JWT contains a set of claims represented as a JSON object,
   then the members of the JSON object represented by the Decoded JWT
   Claims Object decoded from the JWT Payload Segment contain the
   claims.  Note however, that the set of claims a JWT must contain to
   be considered valid is context-dependent and is outside the scope of
   this specification.  When used in a security-related context,
   implementations MUST understand and support all of the claims
   present; otherwise, the JWT MUST be rejected for processing.

   There are three classes of JWT Claim Names: Reserved Claim Names,
   Public Claim Names, and Private Claim Names.

4.1.  Reserved Claim Names

   The following claim names are reserved.  None of the claims defined
   in the table below are intended to be mandatory, but rather, provide



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   a starting point for a set of useful, interoperable claims.  All the
   names are short because a core goal of JWTs is for the tokens
   themselves to be short.

   +-------+---------+--------------+----------------------------------+
   | Claim | JSON    | Claim Syntax | Claim Semantics                  |
   | Name  | Value   |              |                                  |
   |       | Type    |              |                                  |
   +-------+---------+--------------+----------------------------------+
   | exp   | integer | IntDate      | The "exp" (expiration time)      |
   |       |         |              | claim identifies the expiration  |
   |       |         |              | time on or after which the token |
   |       |         |              | MUST NOT be accepted for         |
   |       |         |              | processing.  The processing of   |
   |       |         |              | the "exp" claim requires that    |
   |       |         |              | the current date/time MUST be    |
   |       |         |              | before the expiration date/time  |
   |       |         |              | listed in the "exp" claim.       |
   |       |         |              | Implementers MAY provide for     |
   |       |         |              | some small leeway, usually no    |
   |       |         |              | more than a few minutes, to      |
   |       |         |              | account for clock skew.  This    |
   |       |         |              | claim is OPTIONAL.               |
   | iss   | string  | StringAndURI | The "iss" (issuer) claim         |
   |       |         |              | identifies the principal that    |
   |       |         |              | issued the JWT.  The processing  |
   |       |         |              | of this claim is generally       |
   |       |         |              | application specific.  This      |
   |       |         |              | claim is OPTIONAL.               |
   | aud   | string  | StringAndURI | The "aud" (audience) claim       |
   |       |         |              | identifies the audience that the |
   |       |         |              | JWT is intended for.  The        |
   |       |         |              | principal intended to process    |
   |       |         |              | the JWT MUST be identified by    |
   |       |         |              | the value of the audience claim. |
   |       |         |              | If the principal processing the  |
   |       |         |              | claim does not identify itself   |
   |       |         |              | with the identifier in the "aud" |
   |       |         |              | claim value then the JWT MUST be |
   |       |         |              | rejected.  The interpretation of |
   |       |         |              | the contents of the audience     |
   |       |         |              | value is generally application   |
   |       |         |              | specific.  This claim is         |
   |       |         |              | OPTIONAL.                        |







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   | typ   | string  | String       | The "typ" (type) claim is used   |
   |       |         |              | to declare a type for the        |
   |       |         |              | contents of this JWT.  This      |
   |       |         |              | claim is OPTIONAL.               |
   +-------+---------+--------------+----------------------------------+

                    Table 1: Reserved Claim Definitions

   Additional reserved claim names MAY be defined via the IANA JSON Web
   Token Claims registry, as per Section 10.  The syntax values used
   above and in Table 3 are defined as follows:

   +--------------+----------------------------------------------------+
   | Syntax Name  | Syntax Definition                                  |
   +--------------+----------------------------------------------------+
   | IntDate      | The number of seconds from 1970-01-01T0:0:0Z as    |
   |              | measured in UTC until the desired date/time.  See  |
   |              | RFC 3339 [RFC3339] for details regarding           |
   |              | date/times in general and UTC in particular.       |
   | String       | Any string value MAY be used.                      |
   | StringAndURI | Any string value MAY be used but a value           |
   |              | containing a ":" character MUST be a URI as        |
   |              | defined in RFC 3986 [RFC3986].                     |
   | URI          | A URI as defined in RFC 3986 [RFC3986].            |
   | URL          | A URL as defined in RFC 1738 [RFC1738].            |
   +--------------+----------------------------------------------------+

                                  Table 2

4.2.  Public Claim Names

   Claim names can be defined at will by those using JWTs.  However, in
   order to prevent collisions, any new claim name SHOULD either be
   defined in the IANA JSON Web Token Claims registry or be defined as a
   URI that contains a collision resistant namespace.  Examples of
   collision resistant namespaces include:

   o  Domain Names,

   o  Object Identifiers (OIDs) as defined in the ITU-T X 660 and X 670
      Recommendation series or

   o  Universally Unique IDentifier (UUID) as defined in RFC 4122
      [RFC4122].

   In each case, the definer of the name or value MUST take reasonable
   precautions to make sure they are in control of the part of the
   namespace they use to define the claim name.



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4.3.  Private Claim Names

   A producer and consumer of a JWT may agree to any claim name that is
   not a Reserved Name Section 4.1 or a Public Name Section 4.2.  Unlike
   Public Names, these private names are subject to collision and should
   be used with caution.


5.  JWT Header

   The members of the JSON object represented by the Decoded JWT Header
   Segment describe the signature applied to the JWT Header Segment and
   the JWT Payload Segment and optionally additional properties of the
   JWT.  Implementations MUST understand the entire contents of the
   header; otherwise, the JWT MUST be rejected for processing.

5.1.  Reserved Header Parameter Names

   The following header parameter names are reserved.  All the names are
   short because a core goal of JWTs is for the tokens themselves to be
   short.

   +-----------+--------+--------------+-------------------------------+
   | Header    | JSON   | Header       | Header Parameter Semantics    |
   | Parameter | Value  | Parameter    |                               |
   | Name      | Type   | Syntax       |                               |
   +-----------+--------+--------------+-------------------------------+
   | alg       | string | StringAndURI | The "alg" (algorithm) header  |
   |           |        |              | parameter identifies the      |
   |           |        |              | cryptographic algorithm used  |
   |           |        |              | to secure the JWT.  A list of |
   |           |        |              | reserved alg values is in     |
   |           |        |              | Table 4.  The processing of   |
   |           |        |              | the "alg" (algorithm) header  |
   |           |        |              | parameter, if present,        |
   |           |        |              | requires that the value of    |
   |           |        |              | the "alg" header parameter    |
   |           |        |              | MUST be one that is both      |
   |           |        |              | supported and for which there |
   |           |        |              | exists a key for use with     |
   |           |        |              | that algorithm associated     |
   |           |        |              | with the issuer of the JWT.   |
   |           |        |              | This header parameter is      |
   |           |        |              | REQUIRED.                     |







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   | typ       | string | String       | The "typ" (type) header       |
   |           |        |              | parameter is used to declare  |
   |           |        |              | that this data structure is a |
   |           |        |              | JWT.  If a "typ" parameter is |
   |           |        |              | present, it is RECOMMENDED    |
   |           |        |              | that its value be "JWT".      |
   |           |        |              | This header parameter is      |
   |           |        |              | OPTIONAL.                     |
   | jku       | string | URL          | The "jku" (JSON Key URL)      |
   |           |        |              | header parameter is a URL     |
   |           |        |              | that points to JSON-encoded   |
   |           |        |              | public key certificates that  |
   |           |        |              | can be used to validate the   |
   |           |        |              | signature.  The specification |
   |           |        |              | for this encoding is TBD.     |
   |           |        |              | This header parameter is      |
   |           |        |              | OPTIONAL.                     |
   | kid       | string | String       | The "kid" (key ID) header     |
   |           |        |              | parameter is a hint           |
   |           |        |              | indicating which specific key |
   |           |        |              | owned by the signer should be |
   |           |        |              | used to validate the          |
   |           |        |              | signature.  This allows       |
   |           |        |              | signers to explicitly signal  |
   |           |        |              | a change of key to            |
   |           |        |              | recipients.  Omitting this    |
   |           |        |              | parameter is equivalent to    |
   |           |        |              | setting it to an empty        |
   |           |        |              | string.  The interpretation   |
   |           |        |              | of the contents of the "kid"  |
   |           |        |              | parameter is unspecified.     |
   |           |        |              | This header parameter is      |
   |           |        |              | OPTIONAL.                     |
   | x5u       | string | URL          | The "x5u" (X.509 URL) header  |
   |           |        |              | parameter is a URL that       |
   |           |        |              | points to an X.509 public key |
   |           |        |              | certificate that can be used  |
   |           |        |              | to validate the signature.    |
   |           |        |              | This certificate MUST conform |
   |           |        |              | to RFC 5280 [RFC5280].  This  |
   |           |        |              | header parameter is OPTIONAL. |










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   | x5t       | string | String       | The "x5t" (x.509 certificate  |
   |           |        |              | thumbprint) header parameter  |
   |           |        |              | provides a base64url encoded  |
   |           |        |              | SHA-256 thumbprint (a.k.a.    |
   |           |        |              | digest) of the DER encoding   |
   |           |        |              | of an X.509 certificate that  |
   |           |        |              | can be used to match a        |
   |           |        |              | certificate.  This header     |
   |           |        |              | parameter is OPTIONAL.        |
   +-----------+--------+--------------+-------------------------------+

              Table 3: Reserved Header Parameter Definitions

   Additional reserved header parameter names MAY be defined via the
   IANA JSON Web Token Header Parameters registry, as per Section 10.
   The syntax values used above and in Table 1 are defined in Table 2.

5.2.  Public Header Parameter Names

   Additional header parameter names can be defined by those using JWTs.
   However, in order to prevent collisions, any new header parameter
   name or algorithm value SHOULD either be defined in the IANA JSON Web
   Token Header Parameters registry or be defined as a URI that contains
   a collision resistant namespace.  In each case, the definer of the
   name or value MUST take reasonable precautions to make sure they are
   in control of the part of the namespace they use to define the header
   parameter name.

   New header parameters should be introduced sparingly, as they can
   result in non-interoperable JWTs.  Nonetheless, some extensions
   needed for some use cases may require them, such as an extension to
   enable the inclusion of multiple signatures.

5.3.  Private Header Parameter Names

   A producer and consumer of a JWT may agree to any header parameter
   name that is not a Reserved Name Section 5.1 or a Public Name
   Section 5.2.  Unlike Public Names, these private names are subject to
   collision and should be used with caution.

   New header parameters should be introduced sparingly, as they can
   result in non-interoperable JWTs.


6.  Rules for Creating and Validating a JWT

   To create a JWT one MUST follow these steps:




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   1.  Create the payload content to be encoded as the Decoded JWT
       Payload Segment.  If the payload represents a JWT Claims Object,
       then these steps for creating the Decoded JWT Payload Segment
       also apply:

       *  Create a JSON object containing the desired claims.  Note that
          white space is explicitly allowed in the representation and no
          canonicalization is performed before encoding.

       *  Translate this JSON object's Unicode code points into UTF-8,
          as defined in RFC 3629 [RFC3629].  This is the Decoded JWT
          Payload Segment.

   2.  Base64url encode the Decoded JWT Payload Segment.  This encoding
       becomes the JWT Payload Segment.

   3.  Create a JSON object containing a set of desired header
       parameters.  Note that white space is explicitly allowed in the
       representation and no canonicalization is performed before
       encoding.

   4.  Translate this JSON object's Unicode code points into UTF-8, as
       defined in RFC 3629 [RFC3629].

   5.  Base64url encode the UTF-8 representation of this JSON object as
       defined in this specification (without padding).  This encoding
       becomes a JWT Header Segment.

   6.  Construct a JWT Crypto Segment as defined for the particular
       algorithm being used.  The JWT Signing Input is always the
       concatenation of a JWT Header Segment, a period ('.') character,
       and the JWT Payload Segment.  The "alg" header parameter MUST be
       present in the JSON Header Segment, with the algorithm value
       accurately representing the algorithm used to construct the JWT
       Crypto Segment.

   7.  If the JWT Compact Serialization is being used, then:

       *  Concatenate the JWT Header Segment, the JWT Payload Segment
          and then the JWT Crypto Segment in that order, separating each
          by period characters, to create the JWT.

       Else if the JWT JSON Serialization is being used, then:

       *  Create a JSON object with these three members: a "header"
          member whose value is an array of JWT Header Segments, a
          "payload" member whose value is the JWT Payload Segment, and a
          "signature" member whose value is an array of JWT Crypto



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          Segments.

       *  If more than one signature is present, then repeat steps 3
          through 6 for each header and crypto segment to produce
          additional values for the header and signature arrays.

       *  The header and signature arrays must have the same number of
          values, with each header value and corresponding signature
          value being located at the same array index.

   When validating a JWT the following steps MUST be taken.  If any of
   the listed steps fails then the token MUST be rejected for
   processing.

   1.  If the JWT Compact Serialization is being used, then:

       *  The JWT MUST contain two period characters.

       *  The JWT MUST be split on the two period characters resulting
          in three non-empty segments.  The first segment is the JWT
          Header Segment; the second is the JWT Payload Segment; the
          third is the JWT Crypto Segment.

       Else if the JWT JSON Serialization is being used, then:

       *  The JSON MUST contain the three members "header", "payload",
          and "signature" and MAY contain others, which MUST be ignored.
          The payload member MUST be a string and the header and
          signature members MUST be non-empty arrays of strings with
          equal cardinality.

       *  Use a "header" member array value as the JWT Header Segment;
          use the "payload" member value as the JWT Payload Segment; use
          a "signature" member array value with the same index as the
          "header" member array value used as the JWT Crypto Segment.

   2.  The JWT Payload Segment MUST be successfully base64url decoded
       following the restriction given in this spec that no padding
       characters have been used.

   3.  If the payload represents a JWT Claims Object, then these steps
       for validating the Decoded JWT Payload Segment also apply:

       *  The Decoded JWT Payload Segment, which is the Decoded JWT
          Claims Object, MUST be completely valid JSON syntax conforming
          to RFC 4627 [RFC4627].





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       *  When used in a security-related context, the Decoded JWT
          Claims Object MUST be validated to only include claims whose
          syntax and semantics are both understood and supported.

   4.  The JWT Header Segment MUST be successfully base64url decoded
       following the restriction given in this spec that no padding
       characters have been used.

   5.  The Decoded JWT Header Segment MUST be completely valid JSON
       syntax conforming to RFC 4627 [RFC4627].

   6.  The JWT Crypto Segment MUST be successfully base64url decoded
       following the restriction given in this spec that no padding
       characters have been used.

   7.  The JWT Header Segment MUST be validated to only include
       parameters and values whose syntax and semantics are both
       understood and supported.

   8.  The JWT Crypto Segment MUST be successfully validated against the
       JWT Header Segment and JWT Payload Segment in the manner defined
       for the algorithm being used, which MUST be accurately
       represented by the value of the "alg" header parameter, which
       MUST be present.

   9.  If the JWT JSON Serialization is being used, then repeat steps 4
       to 8 for each element of the header and signature arrays.

   Processing a JWT inevitably requires comparing known strings to
   values in the token.  For example, in checking what the algorithm is,
   the Unicode string encoding "alg" will be checked against the member
   names in the Decoded JWT Header Segment to see if there is a matching
   header parameter name.  A similar process occurs when determining if
   the value of the "alg" header parameter represents a supported
   algorithm.  Comparing Unicode strings, however, has significant
   security implications, as per Section 11.

   Comparisons between JSON strings and other Unicode strings MUST be
   performed as specified below:

   1.  Remove any JSON applied escaping to produce an array of Unicode
       code points.

   2.  Unicode Normalization [USA15] MUST NOT be applied at any point to
       either the JSON string or to the string it is to be compared
       against.





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   3.  Comparisons between the two strings MUST be performed as a
       Unicode code point to code point equality comparison.


7.  Base64url encoding as used by JWTs

   JWTs make use of the base64url encoding as defined in RFC 4648
   [RFC4648].  As allowed by Section 3.2 of the RFC, this specification
   mandates that base64url encoding when used with JWTs MUST NOT use
   padding.  The reason for this restriction is that the padding
   character ('=') is not URL safe.

   For notes on implementing base64url encoding without padding, see
   Appendix B.


8.  Signing JWTs with Cryptographic Algorithms

   JWTs use specific cryptographic algorithms to sign the contents of
   the JWT Header Segment and the JWT Payload Segment.  The use of the
   following algorithms for producing JWTs is defined in this section.
   The table below is the list of "alg" header parameter values reserved
   by this specification, each of which is explained in more detail in
   the following sections:

   +--------------------+----------------------------------------------+
   | Alg Parameter      | Algorithm                                    |
   | Value              |                                              |
   +--------------------+----------------------------------------------+
   | HS256              | HMAC using SHA-256 hash algorithm            |
   | HS384              | HMAC using SHA-384 hash algorithm            |
   | HS512              | HMAC using SHA-512 hash algorithm            |
   | RS256              | RSA using SHA-256 hash algorithm             |
   | RS384              | RSA using SHA-384 hash algorithm             |
   | RS512              | RSA using SHA-512 hash algorithm             |
   | ES256              | ECDSA using P-256 curve and SHA-256 hash     |
   |                    | algorithm                                    |
   | ES384              | ECDSA using P-384 curve and SHA-384 hash     |
   |                    | algorithm                                    |
   | ES512              | ECDSA using P-521 curve and SHA-512 hash     |
   |                    | algorithm                                    |
   +--------------------+----------------------------------------------+

             Table 4: JSON Web Token Reserved Algorithm Values

   Of these algorithms, only HMAC SHA-256 and RSA SHA-256 MUST be
   implemented by conforming implementations.  It is RECOMMENDED that
   implementations also support the ECDSA P-256 SHA-256 algorithm.



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   Support for other algorithms is OPTIONAL.

   The portion of a JWT that is signed is the same for all algorithms:
   the concatenation of the JWT Header Segment, a period ('.')
   character, and the JWT Payload Segment.  This character sequence is
   referred to as the JWT Signing Input.  Note that in the JWT Compact
   Serialization, this corresponds to the portion of the JWT
   representation preceding the second period character.  The UTF-8
   representation of the JWT Signing Input is passed to the respective
   signing algorithms.

8.1.  Signing a JWT with HMAC SHA-256

   Hash based Message Authentication Codes (HMACs) enable one to use a
   secret plus a cryptographic hash function to generate a Message
   Authentication Code (MAC).  This can be used to demonstrate that the
   MAC matches the hashed content, in this case the JWT Signing Input,
   which therefore demonstrates that whoever generated the MAC was in
   possession of the secret.

   The algorithm for implementing and validating HMACs is provided in
   RFC 2104 [RFC2104].  Although any HMAC can be used with JWTs, this
   section defines the use of the SHA-256 cryptographic hash function as
   defined in FIPS 180-3 [FIPS.180-3].  The reserved "alg" header
   parameter value "HS256" is used in the JWT Header Segment to indicate
   that the JWT Crypto Segment contains a base64url encoded HMAC SHA-256
   HMAC value.

   The HMAC SHA-256 MAC is generated as follows:

   1.  Apply the HMAC SHA-256 algorithm to the UTF-8 representation of
       the JWT Signing Input using the shared key to produce an HMAC.

   2.  Base64url encode the HMAC as defined in this document.

   The output is placed in the JWT Crypto Segment for that JWT.

   The HMAC SHA-256 MAC on a JWT is validated as follows:

   1.  Apply the HMAC SHA-256 algorithm to the UTF-8 representation of
       the JWT Signing Input of the JWT using the shared key.

   2.  Base64url encode the previously generated HMAC as defined in this
       document.

   3.  If the JWT Crypto Segment and the previously calculated value
       exactly match, then one has confirmation that the key was used to
       generate the HMAC on the JWT and that the contents of the JWT



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       have not be tampered with.

   4.  If the validation fails, the token MUST be rejected.

   Signing with the HMAC SHA-384 and HMAC SHA-512 algorithms is
   performed identically to the procedure for HMAC SHA-256 - just with
   correspondingly longer key and result values.

8.2.  Signing a JWT with RSA SHA-256

   This section defines the use of the RSASSA-PKCS1-v1_5 signature
   algorithm as defined in RFC 3447 [RFC3447], Section 8.2 (commonly
   known as PKCS#1), using SHA-256 as the hash function.  Note that the
   use of the RSASSA-PKCS1-v1_5 algorithm is described in FIPS 186-3
   [FIPS.186-3], Section 5.5, as is the SHA-256 cryptographic hash
   function, which is defined in FIPS 180-3 [FIPS.180-3].  The reserved
   "alg" header parameter value "RS256" is used in the JWT Header
   Segment to indicate that the JWT Crypto Segment contains an RSA SHA-
   256 signature.

   A 2048-bit or longer key length MUST be used with this algorithm.

   The RSA SHA-256 signature is generated as follows:

   1.  Let K be the signer's RSA private key and let M be the UTF-8
       representation of the JWT Signing Input.

   2.  Compute the octet string S = RSASSA-PKCS1-V1_5-SIGN (K, M) using
       SHA-256 as the hash function.

   3.  Base64url encode the octet string S, as defined in this document.

   The output is placed in the JWT Crypto Segment for that JWT.

   The RSA SHA-256 signature on a JWT is validated as follows:

   1.  Take the JWT Crypto Segment and base64url decode it into an octet
       string S. If decoding fails, then the token MUST be rejected.

   2.  Let M be the UTF-8 representation of the JWT Signing Input and
       let (n, e) be the public key corresponding to the private key
       used by the signer.

   3.  Validate the signature with RSASSA-PKCS1-V1_5-VERIFY ((n, e), M,
       S) using SHA-256 as the hash function.

   4.  If the validation fails, the token MUST be rejected.




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   Signing with the RSA SHA-384 and RSA SHA-512 algorithms is performed
   identically to the procedure for RSA SHA-256 - just with
   correspondingly longer key and result values.

8.3.  Signing a JWT with ECDSA P-256 SHA-256

   The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined by
   FIPS 186-3 [FIPS.186-3].  ECDSA provides for the use of Elliptic
   Curve cryptography, which is able to provide equivalent security to
   RSA cryptography but using shorter key lengths and with greater
   processing speed.  This means that ECDSA signatures will be
   substantially smaller in terms of length than equivalently strong RSA
   Digital Signatures.

   This specification defines the use of ECDSA with the P-256 curve and
   the SHA-256 cryptographic hash function.  The P-256 curve is also
   defined in FIPS 186-3.  The reserved "alg" header parameter value
   "ES256" is used in the JWT Header Segment to indicate that the JWT
   Crypto Segment contains an ECDSA P-256 SHA-256 signature.

   A JWT is signed with an ECDSA P-256 SHA-256 signature as follows:

   1.  Generate a digital signature of the UTF-8 representation of the
       JWT Signing Input using ECDSA P-256 SHA-256 with the desired
       private key.  The output will be the EC point (R, S), where R and
       S are unsigned integers.

   2.  Turn R and S into byte arrays in big endian order.  Each array
       will be 32 bytes long.

   3.  Concatenate the two byte arrays in the order R and then S.

   4.  Base64url encode the 64 byte array as defined in this
       specification.

   The output becomes the JWT Crypto Segment for the JWT.

   The following procedure is used to validate the ECDSA signature of a
   JWT:

   1.  Take the JWT Crypto Segment and base64url decode it into a byte
       array.  If decoding fails, the token MUST be rejected.

   2.  The output of the base64url decoding MUST be a 64 byte array.

   3.  Split the 64 byte array into two 32 byte arrays.  The first array
       will be R and the second S. Remember that the byte arrays are in
       big endian byte order; please check the ECDSA validator in use to



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       see what byte order it requires.

   4.  Submit the UTF-8 representation of the JWT Signing Input, R, S
       and the public key (x, y) to the ECDSA P-256 SHA-256 validator.

   5.  If the validation fails, the token MUST be rejected.

   The ECDSA validator will then determine if the digital signature is
   valid, given the inputs.  Note that ECDSA digital signature contains
   a value referred to as K, which is a random number generated for each
   digital signature instance.  This means that two ECDSA digital
   signatures using exactly the same input parameters will output
   different signatures because their K values will be different.  The
   consequence of this is that one must validate an ECDSA signature by
   submitting the previously specified inputs to an ECDSA validator.

   Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512
   algorithms is performed identically to the procedure for ECDSA P-256
   SHA-256 - just with correspondingly longer key and result values.

8.4.  Additional Algorithms

   Additional algorithms MAY be used to protect JWTs with corresponding
   "alg" header parameter values being defined to refer to them.  Like
   claim names, new "alg" header parameter values SHOULD either be
   defined in the IANA JSON Web Token Algorithms registry or be a URI
   that contains a collision resistant namespace.  In particular, the
   use of algorithm identifiers defined in XML DSIG [RFC3275] and
   related specifications is permitted.


9.  JWT Serialization Formats

   JSON Web Tokens (JWTs) support two serialization formats: the JWT
   Compact Serialization, which is more space efficient and intended for
   uses where the token is passed as a simple string-valued parameter,
   and the JWT JSON Serialization, which is more general, being able to
   contain multiple signatures over the same content.  The two
   serialization formats are intended for use in different contexts.

9.1.  JWT Compact Serialization

   The JWT Compact Serialization represents a JWT as a string consisting
   of three JWT Token Segments: the JWT Header Segment, the JWT Payload
   Segment, and the JWT Crypto Segment, in that order, with the segments
   being separated by period ('.') characters.  It is intended for uses
   where the token is passed as a simple string-valued parameter,
   including in URLs.



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   The Compact Serialization contains only one signature to keep this
   format simple.  The example JWT in Section 3.1 uses the Compact
   Serialization.

9.2.  JWT JSON Serialization

   The JWT JSON Serialization represents a JWT as a JSON object with
   members for each of three kinds of JWT Token Segments: a "header"
   member whose value is a non-empty array of JWT Header Segments, a
   "payload" member whose value is the JWT Payload Segment, and a
   "signature" member whose value is a non-empty array of JWT Crypto
   Segments, where the cardinality of both arrays is the same.

   Unlike the Compact Serialization, JWTs using the JSON Serialization
   MAY contain multiple signatures.  Each signature is represented as a
   JWT Crypto Segment in the "signature" member array.  For each
   signature, there is a corresponding "header" member array element
   that specifies the signature algorithm for that signature, and
   potentially other information as well.  Therefore, the syntax is:
   {"header":["<header 1 contents>",...,"<header N contents>"],
    "payload":"<payload contents>",
    "signature":["<signature 1 contents>",...,"<signature N contents>"]
   }

   The i'th signature is computed on the concatenation of <header i
   contents>.<payload contents>.

   Appendix A.4 contains an example JWT using the JSON Serialization.


10.  IANA Considerations

   This specification calls for:

   o  A new IANA registry entitled "JSON Web Token Claims" for reserved
      claim names is defined in Section 4.1.  Inclusion in the registry
      is RFC Required in the RFC 5226 [RFC5226] sense for reserved JWT
      claim names that are intended to be interoperable between
      implementations.  The registry will just record the reserved claim
      name and a pointer to the RFC that defines it.  This specification
      defines inclusion of the claim names defined in Table 1.

   o  A new IANA registry entitled "JSON Web Token Header Parameters"
      for reserved header parameter names is defined in Section 5.1.
      Inclusion in the registry is RFC Required in the RFC 5226
      [RFC5226] sense for reserved JWT header parameter names that are
      intended to be interoperable between implementations.  The
      registry will just record the reserved header parameter name and a



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      pointer to the RFC that defines it.  This specification defines
      inclusion of the header parameter names defined in Table 3.

   o  A new IANA registry entitled "JSON Web Token Algorithms" for
      reserved values used with the "alg" header parameter values is
      defined in Section 8.4.  Inclusion in the registry is RFC Required
      in the RFC 5226 [RFC5226] sense.  The registry will just record
      the "alg" value and a pointer to the RFC that defines it.  This
      specification defines inclusion of the algorithm values defined in
      Table 4.


11.  Security Considerations

   TBD: Lots of work to do here.  We need to remember to look into any
   issues relating to security and JSON parsing.  One wonders just how
   secure most JSON parsing libraries are.  Were they ever hardened for
   security scenarios?  If not, what kind of holes does that open up?
   Also, we need to walk through the JSON standard and see what kind of
   issues we have especially around comparison of names.  For instance,
   comparisons of claim names and other parameters must occur after they
   are unescaped.  Need to also put in text about: Importance of keeping
   secrets secret.  Rotating keys.  Strengths and weaknesses of the
   different algorithms.

   TBD: Need to put in text about why strict JSON validation is
   necessary.  Basically, that if malformed JSON is received then the
   intent of the sender is impossible to reliably discern.  While in
   non-security contexts it's o.k. to be generous in what one accepts,
   in security contexts this can lead to serious security holes.  For
   example, malformed JSON might indicate that someone has managed to
   find a security hole in the issuer's code and is leveraging it to get
   the issuer to issue "bad" tokens whose content the attacker can
   control.

11.1.  Unicode Comparison Security Issues

   Claim names in JWTs are Unicode strings.  For security reasons, the
   representations of these names must be compared verbatim after
   performing any escape processing (as per RFC 4627 [RFC4627], Section
   2.5).

   This means, for instance, that these JSON strings must compare as
   being equal ("JWT", "\u004aWT"), whereas these must all compare as
   being not equal to the first set or to each other ("jwt", "Jwt",
   "JW\u0074").

   JSON strings MAY contain characters outside the Unicode Basic



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   Multilingual Plane.  For instance, the G clef character (U+1D11E) may
   be represented in a JSON string as "\uD834\uDD1E".  Ideally, JWT
   implementations SHOULD ensure that characters outside the Basic
   Multilingual Plane are preserved and compared correctly;
   alternatively, if this is not possible due to these characters
   exercising limitations present in the underlying JSON implementation,
   then input containing them MUST be rejected.


12.  Open Issues and Things To Be Done (TBD)

   The following items remain to be done in this draft (and related
   drafts):

   o  The specification will be a lot clearer if the signature portions
      are cleanly separated from the claims token format and
      serialization portions.  Having tried it this way and being
      dissatisfied with the sometimes unwieldy readability of the
      result, I plan to perform the separation in the next draft.

   o  Consider whether there is a better term than "Digital Signature"
      for the concept that includes both HMACs and digital signatures
      using public keys.

   o  Consider whether we really want to allow private claim names and
      header parameters that are not registered with IANA and are not in
      collision-resistant namespaces.  Eventually this could result in
      interop nightmares where you need to have different code to talk
      to different endpoints that "knows" about each endpoints' private
      parameters.

   o  Clarify the optional ability to provide type information JWTs
      and/or their segments.  Specifically, clarify the intended use of
      the "typ" Header Parameter and the "typ" claim, whether they
      convey syntax or semantics, and indeed, whether this is the right
      approach.  Also clarify the relationship between these type values
      and MIME [RFC2045] types.

   o  Clarify the semantics of the "kid" (key ID) header parameter.
      Open issues include: What happens if a kid header is received with
      an unrecognized value?  Is that an error?  Should it be treated as
      if it's empty?  What happens if the header has a recognized value
      but the value doesn't match the key associated with that value,
      but it does match another key that is associated with the issuer?
      Is that an error?

   o  The "x5t" parameter is currently specified as "a base64url encoded
      SHA-256 thumbprint of the DER encoding of an X.509 certificate".



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      SHA-1 was traditionally used for certificate digests but
      collisions are possible to create and can be used for denial of
      service attacks within multi-tenant services.  We need to
      understand the compatibility issues of using SHA-256 thumbprints
      instead.  We also likely want to specify the digest algorithm
      explicitly.

   o  Several people have objected to the requirement for implementing
      RSA SHA-256, some because they will only be using HMACs and
      symmetric keys, and others because they only want to use ECDSA
      when using asymmetric keys, either for security or key length
      reasons, or both.  I believe therefore, that we should consider
      changing the MUST for RSA SHA-256 to RECOMMENDED.

   o  Since RFC 3447 Section 8 explicitly calls for people NOT to adopt
      RSASSA-PKCS1 for new applications and instead requests that people
      transition to RSASSA-PSS, we probably need some Security
      Considerations text explaining why RSASSA-PKCS1 is being used
      (it's what's commonly implemented) and what the potential
      consequences are.

   o  Generalize the normative text on signing algorithms so that the
      descriptions apply equally to the use of various key lengths - not
      just HMAC SHA-256, RSA SHA-256, and ECDSA P-256 SHA-256.

   o  Add a table cross-referencing the algorithm name strings used in
      standard software packages and specifications.

   o  Add Security Considerations text on timing attacks.

   o  Finish the Security Considerations section.

   o  Sort out what to do with the IANA registries if this is first
      standardized as an OpenID specification.

   o  Write the related specification for encoding public keys using
      JSON, as per the agreement documented at
      http://self-issued.info/?p=390.  This will be used by the "jku"
      (JSON Key URL) header parameter.

   o  Write the companion encryption specification, per the agreements
      documented at http://self-issued.info/?p=378.


13.  References






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13.1.  Normative References

   [FIPS.180-3]
              National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-3, October 2008.

   [FIPS.186-3]
              National Institute of Standards and Technology, "Digital
              Signature Standard (DSS)", FIPS PUB 186-3, June 2009.

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.




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   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [USA15]    Davis, M., Whistler, K., and M. Duerst, "Unicode
              Normalization Forms", Unicode Standard Annex 15, 09 2009.

13.2.  Informative References

   [CanvasApp]
              Facebook, "Canvas Applications", 2010.

   [JSS]      Bradley, J. and N. Sakimura (editor), "JSON Simple Sign",
              September 2010.

   [MagicSignatures]
              Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic
              Signatures", August 2010.

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005.

   [RFC3275]  Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup
              Language) XML-Signature Syntax and Processing", RFC 3275,
              March 2002.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

   [SWT]      Hardt, D. and Y. Goland, "Simple Web Token (SWT)",
              Version 0.9.5.1, November 2009.

   [W3C.CR-xml11-20021015]
              Cowan, J., "Extensible Markup Language (XML) 1.1", W3C
              CR CR-xml11-20021015, October 2002.


Appendix A.  JWT Examples

A.1.  JWT using HMAC SHA-256






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A.1.1.  Encoding

   The Decoded JWT Payload Segment used in this example is:
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Note that white space is explicitly allowed in Decoded JWT Claims
   Objects and no canonicalization is performed before encoding.  The
   following byte array contains the UTF-8 characters for the Decoded
   JWT Payload Segment:

   [123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10,
   32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56,
   48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97,
   109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111,
   111, 116, 34, 58, 116, 114, 117, 101, 125]

   Base64url encoding the above yields the JWT Payload Segment value:
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The following example JSON header object declares that the data
   structure is a JSON Web Token (JWT) and the JWT Signing Input is
   signed using the HMAC SHA-256 algorithm:
   {"typ":"JWT",
    "alg":"HS256"}

   The following byte array contains the UTF-8 characters for the
   Decoded JWT Header Segment:

   [123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32,
   34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this JWT Header
   Segment value:
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

   Concatenating the JWT Header Segment, a period character, and the JWT
   Payload Segment yields this JWT Signing Input value (with line breaks
   for display purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWT Signing Input is the following
   byte array:

   [101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81,



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   105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74,
   73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51,
   77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67,
   74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84,
   107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100,
   72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76,
   109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73,
   106, 112, 48, 99, 110, 86, 108, 102, 81]

   HMACs are generated using keys.  This example used the key
   represented by the following byte array:

   [3, 35, 53, 75, 43, 15, 165, 188, 131, 126, 6, 101, 119, 123, 166,
   143, 90, 179, 40, 230, 240, 84, 201, 40, 169, 15, 132, 178, 210, 80,
   46, 191, 211, 251, 90, 146, 210, 6, 71, 239, 150, 138, 180, 195, 119,
   98, 61, 34, 61, 46, 33, 114, 5, 46, 79, 8, 192, 205, 154, 245, 103,
   208, 128, 163]

   Running the HMAC SHA-256 algorithm on the UTF-8 representation of the
   JWT Signing Input with this key yields the following byte array:

   [116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173,
   187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83,
   132, 141, 121]

   Base64url encoding the above HMAC output yields the JWT Crypto
   Segment value:
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

   Combining these segments in the order Header.Payload.Signature with
   period characters between the segments yields this complete JWT using
   the JWT Compact Serialization (with line breaks for display purposes
   only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

A.1.2.  Decoding

   Decoding the JWT first requires removing the base64url encoding from
   the JWT Header Segment, the JWT Payload Segment, and the JWT Crypto
   Segment.  We base64url decode the segments per Section 7 and turn
   them into the corresponding byte arrays.  We translate the header
   segment byte array containing UTF-8 encoded characters into the
   Decoded JWT Header Segment string.  Likewise, if the payload
   represents a JWT Claims Object, we translate the payload segment byte



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   array containing UTF-8 encoded characters into a Decoded JWT Claims
   Object string.

A.1.3.  Validating

   Next we validate the decoded results.  Since the "alg" parameter in
   the header is "HS256", we validate the HMAC SHA-256 signature
   contained in the JWT Crypto Segment.  If any of the validation steps
   fail, the token MUST be rejected.

   First, we validate that the decoded JWT Header Segment string is
   legal JSON.

   If the payload represents a JWT Claims Object, we also validate that
   the decoded JWT Payload Segment string is legal JSON.

   To validate the signature, we repeat the previous process of using
   the correct key and the UTF-8 representation of the JWT Signing Input
   as input to a SHA-256 HMAC function and then taking the output and
   determining if it matches the Decoded JWT Crypto Segment.  If it
   matches exactly, the token has been validated.

A.2.  JWT using RSA SHA-256

A.2.1.  Encoding

   The Decoded JWT Payload Segment used in this example is the same as
   in the previous example:
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Since the JWT Payload Segment will therefore be the same, its
   computation is not repeated here.  However, the Decoded JWT Header
   Segment is different in two ways: First, because a different
   algorithm is being used, the "alg" value is different.  Second, for
   illustration purposes only, the optional "typ" parameter is not used.
   (This difference is not related to the signature algorithm employed.)
   The Decoded JWT Header Segment used is:
   {"alg":"RS256"}

   The following byte array contains the UTF-8 characters for the
   Decoded JWT Header Segment:

   [123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this JWT Header
   Segment value:



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   eyJhbGciOiJSUzI1NiJ9

   Concatenating the JWT Header Segment, a period character, and the JWT
   Payload Segment yields this JWT Signing Input value (with line breaks
   for display purposes only):
eyJhbGciOiJSUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWT Signing Input is the following
   byte array:

   [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73,
   49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105,
   74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72,
   65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68,
   65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76,
   121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118,
   98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48,
   99, 110, 86, 108, 102, 81]

   The RSA key consists of a public part (n, e), and a private exponent
   d.  The values of the RSA key used in this example, presented as the
   byte arrays representing big endian integers are:



























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   +-----------+-------------------------------------------------------+
   | Parameter | Value                                                 |
   | Name      |                                                       |
   +-----------+-------------------------------------------------------+
   | n         | [161, 248, 22, 10, 226, 227, 201, 180, 101, 206, 141, |
   |           | 45, 101, 98, 99, 54, 43, 146, 125, 190, 41, 225, 240, |
   |           | 36, 119, 252, 22, 37, 204, 144, 161, 54, 227, 139,    |
   |           | 217, 52, 151, 197, 182, 234, 99, 221, 119, 17, 230,   |
   |           | 124, 116, 41, 249, 86, 176, 251, 138, 143, 8, 154,    |
   |           | 220, 75, 105, 137, 60, 193, 51, 63, 83, 237, 208, 25, |
   |           | 184, 119, 132, 37, 47, 236, 145, 79, 228, 133, 119,   |
   |           | 105, 89, 75, 234, 66, 128, 211, 44, 15, 85, 191, 98,  |
   |           | 148, 79, 19, 3, 150, 188, 110, 155, 223, 110, 189,    |
   |           | 210, 189, 163, 103, 142, 236, 160, 198, 104, 247, 1,  |
   |           | 179, 141, 191, 251, 56, 200, 52, 44, 226, 254, 109,   |
   |           | 39, 250, 222, 74, 90, 72, 116, 151, 157, 212, 185,    |
   |           | 207, 154, 222, 196, 199, 91, 5, 133, 44, 44, 15, 94,  |
   |           | 248, 165, 193, 117, 3, 146, 249, 68, 232, 237, 100,   |
   |           | 193, 16, 198, 182, 71, 96, 154, 164, 120, 58, 235,    |
   |           | 156, 108, 154, 215, 85, 49, 48, 80, 99, 139, 131,     |
   |           | 102, 92, 111, 111, 122, 130, 163, 150, 112, 42, 31,   |
   |           | 100, 27, 130, 211, 235, 242, 57, 34, 25, 73, 31, 182, |
   |           | 134, 135, 44, 87, 22, 245, 10, 248, 53, 141, 154,     |
   |           | 139, 157, 23, 195, 64, 114, 143, 127, 135, 216, 154,  |
   |           | 24, 216, 252, 171, 103, 173, 132, 89, 12, 46, 207,    |
   |           | 117, 147, 57, 54, 60, 7, 3, 77, 111, 96, 111, 158,    |
   |           | 33, 224, 84, 86, 202, 229, 233, 161]                  |
   | e         | [1, 0, 1]                                             |























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   | d         | [18, 174, 113, 164, 105, 205, 10, 43, 195, 126, 82,   |
   |           | 108, 69, 0, 87, 31, 29, 97, 117, 29, 100, 233, 73,    |
   |           | 112, 123, 98, 89, 15, 157, 11, 165, 124, 150, 60, 64, |
   |           | 30, 63, 207, 47, 44, 211, 189, 236, 136, 229, 3, 191, |
   |           | 198, 67, 155, 11, 40, 200, 47, 125, 55, 151, 103, 31, |
   |           | 82, 19, 238, 216, 193, 90, 37, 216, 213, 206, 160, 2, |
   |           | 94, 227, 171, 46, 139, 127, 121, 33, 111, 198, 59,    |
   |           | 234, 86, 39, 83, 180, 6, 68, 198, 161, 81, 39, 217,   |
   |           | 178, 149, 69, 64, 160, 187, 225, 163, 5, 86, 152, 45, |
   |           | 78, 159, 222, 95, 100, 37, 241, 77, 75, 113, 52, 65,  |
   |           | 181, 93, 199, 59, 155, 74, 237, 204, 146, 172, 227,   |
   |           | 146, 126, 55, 245, 125, 12, 253, 94, 117, 129, 250,   |
   |           | 81, 44, 143, 73, 97, 169, 235, 11, 128, 248, 168, 7,  |
   |           | 70, 114, 138, 85, 255, 70, 71, 31, 52, 37, 6, 59,     |
   |           | 157, 83, 100, 47, 94, 222, 30, 132, 214, 19, 8, 26,   |
   |           | 250, 92, 34, 208, 81, 40, 91, 214, 59, 148, 59, 86,   |
   |           | 93, 137, 138, 5, 104, 84, 19, 229, 60, 60, 108, 101,  |
   |           | 37, 255, 31, 227, 78, 61, 220, 112, 240, 213, 100,    |
   |           | 80, 253, 164, 139, 161, 46, 16, 78, 157, 235, 159,    |
   |           | 184, 24, 129, 225, 196, 189, 242, 93, 146, 71, 244,   |
   |           | 80, 200, 101, 146, 121, 104, 231, 115, 52, 244, 65,   |
   |           | 79, 117, 167, 80, 225, 57, 84, 110, 58, 138, 115,     |
   |           | 157]                                                  |
   +-----------+-------------------------------------------------------+

   The RSA private key (n, d) is then passed to the RSA signing
   function, which also takes the hash type, SHA-256, and the UTF-8
   representation of the JWT Signing Input as inputs.  The result of the
   signature is a byte array S, which represents a big endian integer.
   In this example, S is:





















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   +--------+----------------------------------------------------------+
   | Result | Value                                                    |
   | Name   |                                                          |
   +--------+----------------------------------------------------------+
   | S      | [112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45,  |
   |        | 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115,   |
   |        | 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253,  |
   |        | 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, |
   |        | 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, |
   |        | 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198,     |
   |        | 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237,   |
   |        | 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248,  |
   |        | 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, |
   |        | 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230,   |
   |        | 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212,   |
   |        | 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102,    |
   |        | 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, |
   |        | 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, |
   |        | 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145,    |
   |        | 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157,  |
   |        | 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212,  |
   |        | 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, |
   |        | 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33,   |
   |        | 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160,   |
   |        | 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251,  |
   |        | 71]                                                      |
   +--------+----------------------------------------------------------+

   Base64url encoding the signature produces this value for the JWT
   Crypto Segment:
cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw

   Combining these segments in the order Header.Payload.Signature with
   period characters between the segments yields this complete JWT using
   the JWT Compact Serialization (with line breaks for display purposes
   only):
eyJhbGciOiJSUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw

A.2.2.  Decoding

   Decoding the JWT from this example requires processing the JWT Header
   Segment and JWT Payload Segment exactly as done in the first example.





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A.2.3.  Validating

   Since the "alg" parameter in the header is "RS256", we validate the
   RSA SHA-256 signature contained in the JWT Crypto Segment.  If any of
   the validation steps fail, the token MUST be rejected.

   First, we validate that the decoded JWT Header Segment string is
   legal JSON.

   If the payload represents a JWT Claims Object, we also validate that
   the decoded JWT Payload Segment string is legal JSON.

   Validating the JWT Crypto Segment is a little different from the
   previous example.  First, we base64url decode the JWT Crypto Segment
   to produce a signature S to check.  We then pass (n, e), S and the
   UTF-8 representation of the JWT Signing Input to an RSA signature
   verifier that has been configured to use the SHA-256 hash function.

A.3.  JWT using ECDSA P-256 SHA-256

A.3.1.  Encoding

   The Decoded JWT Payload Segment used in this example is the same as
   in the previous examples:
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Since the JWT Payload Segment will therefore be the same, its
   computation is not repeated here.  However, the Decoded JWT Header
   Segment is differs from the previous example because a different
   algorithm is being used.  The Decoded JWT Header Segment used is:
   {"alg":"ES256"}

   The following byte array contains the UTF-8 characters for the
   Decoded JWT Header Segment:

   [123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this JWT Header
   Segment value:
   eyJhbGciOiJFUzI1NiJ9

   Concatenating the JWT Header Segment, a period character, and the JWT
   Payload Segment yields this JWT Signing Input value (with line breaks
   for display purposes only):





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eyJhbGciOiJFUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWT Signing Input is the following
   byte array:

   [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73,
   49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105,
   74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72,
   65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68,
   65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76,
   121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118,
   98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48,
   99, 110, 86, 108, 102, 81]

   The ECDSA key consists of a public part, the EC point (x, y), and a
   private part d.  The values of the ECDSA key used in this example,
   presented as the byte arrays representing big endian integers are:

   +-----------+-------------------------------------------------------+
   | Parameter | Value                                                 |
   | Name      |                                                       |
   +-----------+-------------------------------------------------------+
   | x         | [127, 205, 206, 39, 112, 246, 196, 93, 65, 131, 203,  |
   |           | 238, 111, 219, 75, 123, 88, 7, 51, 53, 123, 233, 239, |
   |           | 19, 186, 207, 110, 60, 123, 209, 84, 69]              |
   | y         | [199, 241, 68, 205, 27, 189, 155, 126, 135, 44, 223,  |
   |           | 237, 185, 238, 185, 244, 179, 105, 93, 110, 169, 11,  |
   |           | 36, 173, 138, 70, 35, 40, 133, 136, 229, 173]         |
   | d         | [142, 155, 16, 158, 113, 144, 152, 191, 152, 4, 135,  |
   |           | 223, 31, 93, 119, 233, 203, 41, 96, 110, 190, 210,    |
   |           | 38, 59, 95, 87, 194, 19, 223, 132, 244, 178]          |
   +-----------+-------------------------------------------------------+

   The ECDSA private part d is then passed to an ECDSA signing function,
   which also takes the curve type, P-256, the hash type, SHA-256, and
   the UTF-8 representation of the JWT Signing Input as inputs.  The
   result of the signature is the EC point (R, S), where R and S are
   unsigned integers.  In this example, the R and S values, given as
   byte arrays representing big endian integers are:










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   +--------+----------------------------------------------------------+
   | Result | Value                                                    |
   | Name   |                                                          |
   +--------+----------------------------------------------------------+
   | R      | [14, 209, 33, 83, 121, 99, 108, 72, 60, 47, 127, 21, 88, |
   |        | 7, 212, 2, 163, 178, 40, 3, 58, 249, 124, 126, 23, 129,  |
   |        | 154, 195, 22, 158, 166, 101]                             |
   | S      | [197, 10, 7, 211, 140, 60, 112, 229, 216, 241, 45, 175,  |
   |        | 8, 74, 84, 128, 166, 101, 144, 197, 242, 147, 80, 154,   |
   |        | 143, 63, 127, 138, 131, 163, 84, 213]                    |
   +--------+----------------------------------------------------------+

   Concatenating the S array to the end of the R array and base64url
   encoding the result produces this value for the JWT Crypto Segment:
DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q

   Combining these segments in the order Header.Payload.Signature with
   period characters between the segments yields this complete JWT using
   the JWT Compact Serialization (with line breaks for display purposes
   only):
eyJhbGciOiJFUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q

A.3.2.  Decoding

   Decoding the JWT from this example requires processing the JWT Header
   Segment and JWT Payload Segment exactly as done in the first example.

A.3.3.  Validating

   Since the "alg" parameter in the header is "ES256", we validate the
   ECDSA P-256 SHA-256 signature contained in the JWT Crypto Segment.
   If any of the validation steps fail, the token MUST be rejected.

   First, we validate that the decoded JWT Header Segment string is
   legal JSON.

   If the payload represents a JWT Claims Object, we also validate that
   the decoded JWT Payload Segment string is legal JSON.

   Validating the JWT Crypto Segment is a little different from the
   first example.  First, we base64url decode the JWT Crypto Segment as
   in the previous examples but we then need to split the 64 member byte
   array that must result into two 32 byte arrays, the first R and the
   second S. We then pass (x, y), (R, S) and the UTF-8 representation of



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   the JWT Signing Input to an ECDSA signature verifier that has been
   configured to use the P-256 curve with the SHA-256 hash function.

   As explained in Section 8.3, the use of the k value in ECDSA means
   that we cannot validate the correctness of the signature in the same
   way we validated the correctness of the HMAC.  Instead,
   implementations MUST use an ECDSA validator to validate the
   signature.

A.4.  JWT using JSON Serialization

   Previous example JWTs shown have used the JWT Compact Serialization.
   This section contains an example JWT using the JWT JSON
   Serialization.  This example demonstrates the capability for
   conveying multiple signatures for the same JWT.

A.4.1.  Encoding

   The Decoded JWT Payload Segment used in this example is the same as
   in the previous examples:
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Two signatures are used in this JWT: an RSA SHA-256 signature, for
   which the header and signature values are the same as in
   Appendix A.2, and an ECDSA P-256 SHA-256 signature, for which the
   header and signature values are the same as in Appendix A.3.  The two
   Decoded JWT Header Segments used are:
   {"alg":"RS256"}

   and:
   {"alg":"ES256"}

   Since the computations for all JWT Token Segments used in this
   example were already presented in previous examples, they are not
   repeated here.

   A JSON Serialization of this JWT is as follows:
{"header":[
  "eyJhbGciOiJSUzI1NiJ9",
  "eyJhbGciOiJFUzI1NiJ9"],
 "payload":"eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ",
 "signature":[
  "cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw",
  "DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q"]
}




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A.4.2.  Decoding

   Decoding the JWT first requires removing the base64url encoding from
   the array of JWT Header Segments, the JWT Payload Segment, and the
   array of JWT Crypto Segments.  We base64url decode the segments per
   Section 7 and turn them into the corresponding byte arrays.  We
   translate the header segment byte arrays containing UTF-8 encoded
   characters into Decoded JWT Header Segment strings.  Likewise, if the
   payload represents a JWT Claims Object, we translate the payload
   segment byte array into a Decoded JWT Claims Object string.

A.4.3.  Validating

   If any of the validation steps fail, the token MUST be rejected.

   First, we validate that the header and signature arrays contain the
   same number of elements.

   Next, we validate that the Decoded JWT Header Segment strings are all
   legal JSON.

   If the payload represents a JWT Claims Object, we also validate that
   the decoded JWT Payload Segment string is legal JSON.

   Finally, for each Decoded JWT Header Segment, we validate the
   corresponding signature using the algorithm specified in the "alg"
   parameter, which must be present.


Appendix B.  Notes on implementing base64url encoding without padding

   This appendix describes how to implement base64url encoding and
   decoding functions without padding based upon standard base64
   encoding and decoding functions that do use padding.

   To be concrete, example C# code implementing these functions is shown
   below.  Similar code could be used in other languages.














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   static string base64urlencode(byte [] arg)
   {
     string s = Convert.ToBase64String(arg); // Standard base64 encoder
     s = s.Split('=')[0]; // Remove any trailing '='s
     s = s.Replace('+', '-'); // 62nd char of encoding
     s = s.Replace('/', '_'); // 63rd char of encoding
     return s;
   }

   static byte [] base64urldecode(string arg)
   {
     string s = arg;
     s = s.Replace('-', '+'); // 62nd char of encoding
     s = s.Replace('_', '/'); // 63rd char of encoding
     switch (s.Length % 4) // Pad with trailing '='s
     {
       case 0: break; // No pad chars in this case
       case 2: s += "=="; break; // Two pad chars
       case 3: s += "="; break; // One pad char
       default: throw new System.Exception(
         "Illegal base64url string!");
     }
     return Convert.FromBase64String(s); // Standard base64 decoder
   }

   As per the example code above, the number of '=' padding characters
   that needs to be added to the end of a base64url encoded string
   without padding to turn it into one with padding is a deterministic
   function of the length of the encoded string.  Specifically, if the
   length mod 4 is 0, no padding is added; if the length mod 4 is 2, two
   '=' padding characters are added; if the length mod 4 is 3, one '='
   padding character is added; if the length mod 4 is 1, the input is
   malformed.

   An example correspondence between unencoded and encoded values
   follows.  The byte sequence below encodes into the string below,
   which when decoded, reproduces the byte sequence.
   3 236 255 224 193
   A-z_4ME


Appendix C.  Relationship of JWTs to SAML Tokens

   SAML 2.0 [OASIS.saml-core-2.0-os] provides a standard for creating
   tokens with much greater expressivity and more security options than
   supported by JWTs.  However, the cost of this flexibility and
   expressiveness is both size and complexity.  In addition, SAML's use
   of XML [W3C.CR-xml11-20021015] and XML DSIG [RFC3275] only



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   contributes to the size of SAML tokens.

   JWTs are intended to provide a simple token format that is small
   enough to fit into HTTP headers and query arguments in URIs.  It does
   this by supporting a much simpler token model than SAML and using the
   JSON [RFC4627] object encoding syntax.  It also supports securing
   tokens using Hash-based Message Authentication Codes (HMACs) and
   digital signatures using a smaller (and less flexible) format than
   XML DSIG.

   Therefore, while JWTs can do some of the things SAML tokens do, JWTs
   are not intended as a full replacement for SAML tokens, but rather as
   a compromise token format to be used when space is at a premium.


Appendix D.  Relationship of JWTs to Simple Web Tokens (SWTs)

   Both JWTs and Simple Web Tokens SWT [SWT], at their core, enable sets
   of claims to be communicated between applications.  For SWTs, both
   the claim names and claim values are strings.  For JWTs, while claim
   names are strings, claim values can be any JSON type.  Both token
   types offer cryptographic protection of their content: SWTs with HMAC
   SHA-256 and JWTs with a choice of algorithms, including HMAC SHA-256,
   RSA SHA-256, and ECDSA P-256 SHA-256.  The signed content of a SWT
   must be a set of claims, whereas the payload of a JWT, in general,
   can be any base64url encoded content.


Appendix E.  Acknowledgements

   The authors acknowledge that the design of JWTs was intentionally
   influenced by the design and simplicity of Simple Web Tokens [SWT].
   Solutions for signing JSON tokens were also previously explored by
   Magic Signatures [MagicSignatures], JSON Simple Sign [JSS], and
   Canvas Applications [CanvasApp], all of which influenced this draft.


Appendix F.  Document History

   -01

   o  Draft incorporating consensus decisions reached at IIW.

   -00

   o  Public draft published before November 2010 IIW based upon the
      JSON token convergence proposal incorporating input from several
      implementers of related specifications.



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Authors' Addresses

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/


   Dirk Balfanz
   Google

   Email: balfanz@google.com


   John Bradley
   independent

   Email: ve7jtb@ve7jtb.com


   Yaron Y. Goland
   Microsoft

   Email: yarong@microsoft.com


   John Panzer
   Google

   Email: jpanzer@google.com


   Nat Sakimura
   Nomura Research Institute

   Email: n-sakimura@nri.co.jp


   Paul Tarjan
   Facebook

   Email: paul.tarjan@facebook.com








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