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SIPCore                                              R. Shekh-Yusef, Ed.
Internet-Draft                                                     Avaya
Updates: 3261 (if approved)                                   V. Pascual
Intended status: Standards Track                                  Oracle
Expires: September 9, 2016                                   C. Holmberg
                                                                Ericsson
                                                           March 8, 2016


              The Session Initiation Protocol (SIP) OAuth
                    draft-yusef-sipcore-sip-oauth-03

Abstract

   This document defines an authorization framework for SIP that is
   based on the OAuth 2.0 framework, and adds a simple identity layer on
   top of that, based on the OpenID Connect Core 1.0, to enable Clients
   to verify the identity of the End-User based on the authentication
   performed by an Authorization Server, as well as to obtain basic
   profile information about the End-User.

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
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   This Internet-Draft will expire on September 9, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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   This document may contain material from IETF Documents or IETF
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   4
       1.3.1.  Enterprise SSO  . . . . . . . . . . . . . . . . . . .   4
       1.3.2.  3GPP  . . . . . . . . . . . . . . . . . . . . . . . .   5
       1.3.3.  Confidential SIP Hardphone  . . . . . . . . . . . . .   5
       1.3.4.  Public SIP Hardphone  . . . . . . . . . . . . . . . .   5
       1.3.5.  SIP SSO . . . . . . . . . . . . . . . . . . . . . . .   6
     1.4.  Roles . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.5.  ID Token  . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.6.  Authentication Types  . . . . . . . . . . . . . . . . . .   8
   2.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.1.  Single Sign-On  . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Service Authorization . . . . . . . . . . . . . . . . . .   8
     2.3.  Third-Party Authentication  . . . . . . . . . . . . . . .   9
   3.  Authorization Code Grant type . . . . . . . . . . . . . . . .   9
     3.1.  Operations Overview . . . . . . . . . . . . . . . . . . .   9
     3.2.  Authentication  . . . . . . . . . . . . . . . . . . . . .  12
     3.3.  Registration  . . . . . . . . . . . . . . . . . . . . . .  13
     3.4.  Subsequent Requests . . . . . . . . . . . . . . . . . . .  14
     3.5.  Token Refresh . . . . . . . . . . . . . . . . . . . . . .  14
     3.6.  Services  . . . . . . . . . . . . . . . . . . . . . . . .  15
   4.  Implicit Grant Type . . . . . . . . . . . . . . . . . . . . .  16
     4.1.  OAuth Implicit Grant  . . . . . . . . . . . . . . . . . .  16
       4.1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . .  16
       4.1.2.  Authentication  . . . . . . . . . . . . . . . . . . .  17
       4.1.3.  Registration  . . . . . . . . . . . . . . . . . . . .  18
       4.1.4.  Subsequent Requests . . . . . . . . . . . . . . . . .  19



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       4.1.5.  Services  . . . . . . . . . . . . . . . . . . . . . .  19
     4.2.  OpenID Implicit Grant . . . . . . . . . . . . . . . . . .  20
   5.  Resource Owner Password Credentials Grant type  . . . . . . .  21
     5.1.  Operations Overview . . . . . . . . . . . . . . . . . . .  21
     5.2.  Registration and Acquiring Tokens . . . . . . . . . . . .  22
     5.3.  Discarding Credentials  . . . . . . . . . . . . . . . . .  23
     5.4.  Token Refresh . . . . . . . . . . . . . . . . . . . . . .  23
     5.5.  Authenticated Requests  . . . . . . . . . . . . . . . . .  23
     5.6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  24
   6.  Outbound  . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     6.1.  Authorization Code Grant type . . . . . . . . . . . . . .  25
     6.2.  Resource Owner Password Credentials Grant type  . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  25
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   The SIP protocol [RFC3261] uses the framework used by the HTTP
   protocol for authenticating users, which is a simple challenge-
   response authentication mechanism that allows a server to challenge a
   client request and allows a client to provide authentication
   information in response to that challenge.

   The SIP protocol does not have an authorization framework to allow
   the system to control access to various services provided by the
   system.

   OAuth 2.0 [RFC6749] defines a token based authorization framework to
   allow clients to access resources on behalf of their user.  It also
   defines four types of authorization grants, which the client uses to
   request the access token.

   The OpenID Connect 1.0 [OPENID] specifications defines a simple
   identity layer on top of the OAuth 2.0 protocol, which enables
   Clients to verify the identity of the End-User based on the
   authentication performed by an Authorization Server, as well as to
   obtain basic profile information about the End-User.

   This document defines an authorization framework for SIP that is
   based on the OAuth 2.0 framework, and adds the identity layer on top
   of that, based on the OpenID Connect Core 1.0 specification







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1.1.  Terminology

   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 [RFC2119].

1.2.  Definitions

      Types of SIP services:

      *  Basic SIP Services: make/receive call, transfer, call forward,
         etc.

      *  Advanced SIP Services: services provided by SIP application
         servers, e.g.  Voice Mail, Conference Services, Presence, IM,
         ...

      Single Sign-On (SSO)

         SSO is a property that allows the user to be authenticated once
         and as a result have access to multiple services in the system.

      Authentication

         The process of verifying the identity of a user trying to get
         access to some network services.

      Authorization

         The process of controlling an authenticated user access to
         network services and the level of service provided to the user.


1.3.  Use Cases

1.3.1.  Enterprise SSO

   An enterprise is interested in providing its users with an SSO
   capability to the various corporate services.  The enterprise has an
   authorization server for controlling the user access to their network
   and would like to extend that existing authorization server to
   control the user access to the various services provided by their SIP
   network.

   The user is expected to provide his corporate credentials to login to
   the corporate network and get different types of services, regardless
   of the protocol used to provide the service, and without the need to
   create different accounts for these different types of services.



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1.3.2.  3GPP

   The 3GPP network has a requirement to allow a user using a WebRTC IMS
   Client (WIC) to authenticate to a WebRTC Authorization Function (WAF)
   and in response be given an access token that allows the user to
   register and get service from the 3GPP SIP network.

   The WIC downloads an IMS webpage from the WebRTC Web Server Function
   (WWSF) using HTTP.  The WIC then requests an access token from the
   WAF using HTTP, which the WIC then uses to register to the SIP
   network throught the P-CSCF enhanced for WebRTC (eP-CSCF) element.


1.3.3.  Confidential SIP Hardphone

   A SIP hardphone with rich UI, that has the capability to maintain the
   confidentiality of user's crecentials, is used to authenticate to an
   authorization server, get a token, and use that token to register and
   get service from the SIP network.

   When the phone interacts with the authorization server and gets
   challenged to provide credentials, the phone will prompt the user to
   enter his credentials which will be used to authenticate to the
   authorization server.


1.3.4.  Public SIP Hardphone

   A SIP hardphone with limited UI capabilities, that is incapable of
   maintaining confidentiality of user's crecentials, is used to
   register with the SIP network by providing an access code obtaied
   from an authorization server.

   When the phone interacts with the SIP network without providing any
   credentials, the phone gets challenged to provide proper credentials.

   The user will then use an out of band method, e.g browser, to
   authenticate to the authorization server and get a short-lived
   numeric access code.

   The user will then use the phone's keypad to provide the numeric
   access code to the SIP phone.  The phone will then use the access
   code to register and get service from the SIP network.  The SIP Proxy
   will exchange the access code with access token from the
   authorization server.






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1.3.5.  SIP SSO

   An enterprise is interested in providing its users with an SSO
   capability to the various corporate SIP services.

   The enterprise wants to control the services provided to their SIP
   users and the level of service provided to the user by their SIP
   application servers without the need to create different accounts for
   these services.

   The enterprise wants to utilize an existing authentication mechanism
   provided by SIP, but would like to be able to control who gets access
   to what service and when.

   The user is expected to use his SIP credentials to login to the SIP
   network and get access to the basic services, and to get access to
   the services provided by the various SIP application servers without
   being challenged to provide credentials for each type of service.

































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1.4.  Roles

      resource owner

         An entity capable of granting access to a protected resource.
         When the resource owner is a person, it is referred to as an
         end-user.

         In a typical SIP network, it is the management element in the
         system that acts as a resource owner.

      resource server

         The server hosting the protected resources or services, capable
         of accepting and responding to protected resource and services
         requests using access tokens.

      OAuth 2.0 client

         An application making protected resource requests on behalf of
         the resource owner and with its authorization.  The term
         "client" does not imply any particular implementation
         characteristics (e.g., whether the application executes on a
         server, a desktop, or other devices).

      SIP client

         An application making requests to access SIP services on behalf
         of the end-user.

      authorization server

         The server issuing tokens to the OAuth 2.0 client or SIP Client
         after successfully authenticating the resource owner and
         obtaining authorization.

      proof-of-possession (pop)

         A hash used by one party to prove to another party that it is
         in possession of some shared credentials, without sending the
         credentials on the wire.


1.5.  ID Token

   ID token, as defined in the OpenID document, is a security token that
   contains claims about the authentication of an end-user by an
   authorization server.



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1.6.  Authentication Types

   There are two types of user authentications in SIP:

   o  Proxy-to-User: which allows a server that is providing a service
      to authenticate the identity of a user before providing the
      service.

   o  User-to-User: which allows a user recieving a request to
      authenticate the identity of the remote user before processing the
      request.

   The mechanism defined in this document addresses the proxy-to-user
   authentication only.  For user-to-user authentication refer to the
   mechanism defined in [STIR].


2.  Benefits

   This section describes the benefit of this authorization framework:

2.1.  Single Sign-On

   With the existing mechanism, the proxy and application servers might
   need to challenge many of the requests sent by a client, which adds
   traffic that could be avoided with this authorization mechanism.

   Single Sign-On is a property that allows the user to be authenticated
   once and as a result have access to multiple services in the system.

   This authorization mechanism would enable Single Sign-On, as the user
   will be authenticated once and as a result given a token and a
   refresh token to allow the user access to various services based on
   the token scope.

2.2.  Service Authorization

   This authorization mechanism allows the system to centrally control
   the services provided to the user, e.g conference services, voice
   mail, etc.  The mechanism also allow control over the level of
   services provided to the user; for example, if the user is given
   access to conference services, the system controls whether the user
   gets access to video conference services or only audio conference
   services.







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2.3.  Third-Party Authentication

   This authorization mechanism allows the user to be authenticated and
   obtain tokens using some Third-Party Authorization mechanism and
   still get services from the system.


3.  Authorization Code Grant type

3.1.  Operations Overview

   The following figure provides a high level view of flow of messages
   for the Authorization Code Grant type:


   Authentication
   --------------

   User                            Proxy                   Authorization
   Agent                                                          Server
   ---------------------------------------------------------------------
     |                               |                               |
     | F1 REGISTER                   |                               |
     |------------------------------>|                               |
     |                        F2 401 |                               |
     |<------------------------------|                               |
     |                               |                               |
     | F3 GET /authorize?response_type=code&...                      |
     |-------------------------------------------------------------->|
     |                               |                        F4 401 |
     |<--------------------------------------------------------------|
     |                               |                               |
     |                               |                               |
   o master-key = HMAC-SHA256(HA1, realm + nonce)                    |
     |                               |                               |
     | F5 GET /authorize?response_type=code&... with credentials     |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |                               |
     |                      o master-key=HMAC-SHA256(HA1, realm + nonce)
     |                               |                               |
     |                               |                 F6 200 [code] |
     |<--------------------------------------------------------------|
     |                               |                               |
     |                               |                               |






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   Registration
   ------------

   User                            Proxy                   Authorization
   Agent                                                          Server
   ---------------------------------------------------------------------
     |                               |                               |
     | F7 REGISTER code, pop         |                               |
     |------------------------------>|                               |
     |                               | F8 POST /token [code]         |
     |                               |------------------------------>|
     |                               |                               |
     |                               | F9 200 OK [ id-token,         |
     |                               |             access_token,     |
     |                               |             refresh_token]    |
     |                               |<------------------------------|
     |                               |                               |
     |                               |                               |
     |                               | F10 GET /userinfo [access_token]
     |                               |------------------------------>|
     |                               |                               |
     |                               | F11 200 OK [ user-info,       |
     |                               |             master-key]       |
     |                               |<------------------------------|
     |                               |                               |
     |                    F12 200 OK |                               |
     |<------------------------------|                               |
     |                               |                               |
     |                               |                               |



   Subsequent Requests
   -------------------

     |                               |                               |
   o pop = HMAC-SHA256(master-key, digest-string)                    |
     |                               |                               |
     | F13 INVITE pop                |                               |
     |------------------------------>|                               |
     |                               |                               |
     |                               |                               |
     |               o The proxy verifies the pop.                   |
     |                               |                               |
     |              F14 180 Ringing  |                               |
     |<------------------------------|                               |
     |                               |                               |




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   Token Refresh
   -------------

   User                            Proxy                   Authorization
   Agent                                                          Server
   ---------------------------------------------------------------------
     |                               |                               |
     |                               | F15 POST /token               |
     |                               |   [ grant_type=refresh_token& |
     |                               |     refresh_token=<ref_token> |
     |                               |------------------------------>|
     |                               |                               |
     |                               |  F16 200 OK [ access_token,   |
     |                               |               refresh_token ] |
     |                               |<------------------------------|
     |                               |                               |
     |                               |                               |



   The UA initially sends a REGISTER request (F1) without providing any
   credentials.

   The proxy challenges the UA by responding with 401 (F2) that includes
   the address of the Authorization Server.

   [[OPEN ISSUE]] How should the UA be redirected to the Authorization
   Server: 1.  New SIP parameter? 2.  Extend the Bearer scheme? 3.
   Define a new Scheme?

   The UA will then contact the Authorization Server without providing
   any credentials in the first request (F3).  The Authorization Server
   challenges the request using the Digest scheme (F4), and the client
   retries the request (F5) and provides the user's credentials.

   The Authorization Server verifies the request from the client; if the
   verification is successful, the Authorization Server responds with
   200 OK (F6) and includes a code in the body part.

   The UA then retries the request (F7) and include the code in the body
   of the request.  The proxy then contacts the Authorization Server and
   exchanges the code for tokens (F8 and F9), and gets the user
   information (F10 and F11).  The proxy then sends 200 OK to the UA to
   complete the registration process.







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3.2.  Authentication

   The UA initiates the process by sending a REGISTER request (F1) to
   the proxy.  The proxy will redirect the UA to the Authorization
   Server by responding with 401 (F2) that includes the address of the
   Authorization Server in the form of an HTTP URI.

   The UA constructs the initial request (F3) to the Authorization
   Server without providing any user credentials, but with the following
   URI parameters in the query component:

   response_type (REQUIRED)

      Value MUST be set to "code".

   user_id (REQUIRED)

      The user's identification with the Authorization Server.

   scope (OPTIONAL)

      The scope of the access request

   state (RECOMMENDED)

      The value of this parameter is a nonce created by the client to
      prevent replay attack.  The nonce is a uniquely generated value
      for each request.  This parameter might not be included with the
      initial request that does not include credentials (F3).

   The Authorization Server uses the user identification specified in
   the user_id parameter to verify that the user has an account in the
   system, and then challenges the request by responding with 401 (F4)
   with Digest scheme.

   The UA will generate a master-key that is based on an HMAC-Hash
   algorithm, e.g.  HMAC-SHA256, that takes an input the user's HA1 and
   the concatenation of realm and nonce received in the challenge from
   the server.

   The UA will then send a new authorization request (F5), but this time
   include the credentials requested by the server.  The UA will use the
   same parameters values used in the initial authorization request with
   the exception of the state parameter which will get a new nonce
   value.

   When the server receives the request with the credentials (F5), the
   server will verify the digest provided by the UA; if that is



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   successful, the server will respond with 200 OK (F6) and include a
   code in the body of the response with the following parameters:

   grant_type (REQUIRED)

      Value MUST be set to "authorization_code".

   code (REQUIRED)

      The authorization code received from the authorization server.

   The server then generates a master-key that is based on an HMAC-Hash
   algorithm, e.g.  HMAC-SHA256, that takes an input the user's HA1, and
   the concatenation of realm and nonce sent in the challenge (F4) to
   the client.


3.3.  Registration

   The UA will send a new REGISTER request (F7) and include the code in
   the body of the request with the following parameters:

   grant_type (REQUIRED)

      Value MUST be set to "authorization_code".

   code (REQUIRED)

      The authorization code received from the authorization server.

   The proxy sends a POST request (F8) to the Authorization Server and
   include the following parameters in the body:

   grant_type (REQUIRED)

      Value MUST be set to "authorization_code".

   code (REQUIRED)

      The authorization code received from the authorization server.

   If the request is valid and authorized, the authorization server
   responds with a 200 OK (F9) with id_token, access token, and
   refresh_token in the body.

   The UA sends a GET request (F10) to the Authorization Server to fetch
   the user information, and includes the access token in the body of
   the request.  In response the Autorization Server will respond with



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   200 OK and include the user information and the master-key associated
   with the user in the body part.

   The proxy then responds with 200 OK (F12) to the UA to complete the
   registration process.


3.4.  Subsequent Requests

   When the UA wants to send any request to the proxy, it MUST include
   the Authorization header and use the Bearer scheme to carry the
   proof-of-possession of the master-key.

   The pop is calculated using the master-key as follows:

      pop = HMAC-SHA256(master-key, digest-string)

   The following is an example of an Authorization header with Bearer
   scheme:

      Authorization: Bearer pop=<pop>

   See rfc4474, section 9, for the SIP headers to hash to create digest-
   string.

   [[OPEN ISSUE]] The Bearer scheme is used to deliver tokens without
   providing any proof of possession.  We probably need to use different
   scheme later on.


3.5.  Token Refresh

   The proxy makes a refresh request to the Authorization Server by
   sending a refresh POST request (F13) that includes a body with the
   grant_type and the refresh_token.

   For example:

      grant_type=refresh_token&refresh_token=<refresh_token>

   If the proxy fails to refresh the token, then it MUST challenge the
   next request from the UA, and as a result the UA MUST go through the
   authorization process again to obtain new tokens.








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3.6.  Services

   When the UA tries to access a service on behalf of a user, e.g.
   Voice Mail Service, the proxy forwards the request to the server
   providing the service and MUST include an Authorization header with
   the Bearer scheme that carries the token needed to get service, as
   follows:

      Authorization: Bearer token=<token>










































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4.  Implicit Grant Type

   The impicit grant type is used by the SIP UA to directly obtain
   access tokens from the Authorization Server to be able to register
   and get service from the SIP network.

   This grant type does not support the issuance of refresh tokens,
   which means that the SIP UA must re-authenticate again to the
   Authorization Server to get a new token before the current token
   expires.


4.1.  OAuth Implicit Grant

4.1.1.  Overview

   The following figure provides a high level view of flow of messages
   for the OAuth Implicit Grant type:


   Authentication
   --------------

   User                            Proxy                   Authorization
   Agent                                                          Server
   ---------------------------------------------------------------------
     |                               |                               |
     | F1 GET /authorize?response_type=token...                      |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |                        F2 401 |
     |<--------------------------------------------------------------|
     |                               |                               |
     |                               |                               |
     | F3 GET /authorize?response_type=token +credentials            |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |      F4 200 OK [access_token] |
     |<--------------------------------------------------------------|
     |                               |                               |











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   Registration
   ------------

     |                               |                               |
     | F5 REGISTER username@domain.com, access_token                 |
     |------------------------------>|                               |
     |                               |    F6 POST /introspect        |
     |                               |        [token=<access_token>] |
     |                               |------------------------------>|
     |                               |                               |
     |                               |                     F7 200 OK |
     |                               |<------------------------------|
     |                     F8 200 OK |                               |
     |<------------------------------|                               |
     |                               |                               |



4.1.2.  Authentication

   The UA starts the process by sending an HTTP GET request to the
   Authorization Server without providing any credentials in the first
   request (F1).

   The UA constructs the initial request (F1) to the Authorization
   Server with the following URI parameters in the query component:

   response_type (REQUIRED)

      Value MUST be set to "token".

   user_id (REQUIRED)

      The user's identification with the Authorization Server.

   scope (OPTIONAL)

      The scope of the access request.


   The Authorization Server challenges the request using the Digest
   scheme (F2).  The client retries the request (F3) and provides the
   user's credentials.  In response the Authorization Server responds
   with 200 OK (F4) with the Access Token in the body.







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4.1.3.  Registration

   The UA starts the registration process with the SIP proxy by sending
   a REGISTER request (F5) with the access token it obtained in the
   previous steps (F1-F4).

   The UA adds the following parameters to the body of the REGISTER
   request:

   access_token (REQUIRED)

      The access token issued by the authorization server.

   token_type (REQUIRED)

      The type of the token issued by the authorization server.  Value
      is case insensitive.

   expires (RECOMMENDED)

      The lifetime in seconds of the access token.

   scope (OPTIONAL)

      The scope of the access request.


   If introspection is used [RFC7662], then the proxy validates the
   access token by sending an HTTP POST request (F6), with the
   parameters sent as "application/x-www-form-urlencoded" data, to the
   Authorization Server and include the following parameters:

   token (REQUIRED)

      The string value of the token.

   token_type_hint (OPTIONAL)

      A hint about the type of the token submitted for introspection.












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   Authorization Server then validates the request and responds with 200
   OK (F7), with a JSON object in the body with the following
   parameters:

   active (REQUIRED)

      Boolean indicator of whether or not the presented token is
      currently active.

   scope (OPTIONAL)

      The scope of the access request.

   Other parameters

      TBD.


4.1.4.  Subsequent Requests

   All subsequent requests from the UA MUST include a valid access
   token.  The UA MUST obtain a new access token before the access token
   expiry period to continue to get service from the system.

4.1.5.  Services

   When the proxy forwards a request from a UA to an application server,
   it makes sure to keep the access token and scope in the message to
   allow the application server to provide the proper service to the
   user.





















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4.2.  OpenID Implicit Grant

   The following figure provides a high level view of flow of messages
   for the OpenID Implicit Grant type:


   User                            Proxy                   Authorization
   Agent                                                          Server
   ---------------------------------------------------------------------
     |                               |                               |
     | F1 GET /authorize?response_type=id_token%20token...           |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |                        F2 401 |
     |<--------------------------------------------------------------|
     |                               |                               |
     | F3 GET /authorize?response_type=id_token%20token +credentials |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |   F4 200 OK [ id-token,       |
     |                               |               access_token]   |
     |<--------------------------------------------------------------|
     |                               |                               |
     | F5 GET /userinfo [access_token]                               |
     |-------------------------------------------------------------->|
     |                               |                               |
     |                               |        F6 200 OK [ user-info] |
     |<--------------------------------------------------------------|
     |                               |                               |
     | F7 REGISTER username@domain.com, access_token                 |
     |------------------------------>|                               |
     |                               |                               |
     |                               |    F8 POST /authorize         |
     |                               |         [token=access_token ] |
     |                               |------------------------------>|
     |                               |                               |
     |                               |     F9 200 OK                 |
     |                               |<------------------------------|
     |                               |                               |
     |                    F10 200 OK |                               |
     |<------------------------------|                               |
     |                               |                               |









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5.  Resource Owner Password Credentials Grant type

5.1.  Operations Overview

   The following figure provides a high level view of flow of messages
   for the Resource Owner Password Credentials Grant type:


     UA                                                           Proxy
   --------------------------------------------------------------------
     |                                                              |
     | F1 REGISTER                                                  |
     |------------------------------------------------------------->|
     |                                                              |
     |                              F2 401 WWW-Authenticate: Digest |
     |<-------------------------------------------------------------|
     |                                                              |
     |                                                              |
   o master-key = HMAC-SHA256(HA1, realm + nonce)                   |
     |                                                              |
     | F3 REGISTER with Authorization                               |
     |------------------------------------------------------------->|
     |                                                              |
     |                                                              |
     |                    o master-key = HMAC-SHA256(HA1, realm + nonce)
     |                                                              |
     |                              F4 200 OK [token, expires, ...] |
     |<-------------------------------------------------------------|
     |                                                              |
     |                                                              |
   o pop = HMAC-SHA256(master-key, token + digest-string)           |
     |                                                              |
     | F5 INVITE token, pop                                         |
     |------------------------------------------------------------->|
     |                                                              |
     |                                    o The server verifies the pop.
     |                                                              |
     |                                               F6 180 Ringing |
     |<-------------------------------------------------------------|
     |                                                              |



   During registration the UA initially sends a REGISTER request (F1)
   without providing any credentials.

   The proxy then challenges the UA by responding with 401 (F2) that
   includes the Digest scheme in the www-authenticate header.



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   The UA will generate a master-key that is based on an HMAC-Hash
   algorithm, e.g.  HMAC-SHA256, that takes an input the user's HA1 and
   the concatenation of realm and nonce received in the challenge from
   the server.  The UA will continue to use the existing operation of
   handling the Digest challenge and then sends a new REGISTER request
   (F3) with the credentials to the server.

   When the server receives the request with the credentials (F3), the
   server will verify the digest provided by the UA; if that is
   successful, the server will accept the registration (F4) and include
   the details of the token in the response.

   The server then generates a master-key that is based on an HMAC-Hash
   algorithm, e.g.  HMAC-SHA256, that takes an input the user's HA1, and
   the concatenation of realm and nonce sent in the challenge to the
   client.

   At the end of the above process the UA would have registered with the
   proxy and both the UA and the proxy would have created the same
   master-key without sending the master-key on the wire.

   Later when the UA wants to send a request to the proxy it MUST always
   include the token and SHOULD include the pop as defined in section
   4.6.

5.2.  Registration and Acquiring Tokens

   The UA MUST request the access token during the registration process
   with the proxy, by including a body with the grant_type as
   "password".  Initially, the UA sends a REGISTER request without
   providing any credentials.

   The proxy MUST then challenge the UA by responding with 401 with the
   Digest scheme in the WWW-Authenticate header.

   When the UA gets challenged by the proxy to provide its credentials,
   the UA MUST include its credentials in the new REGISTER request in
   the authorization header as it is done with the existing mechanism,
   and MUST include a body with the grant_type as "password".

   In addition, the UA MUST generate a master-key as follows:

      master-key = HMAC-SHA256(HA1, realm + nonce)

   Where

   o  HA1 - this is the user's H(A1) as defined in [DIGEST].




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   o  realm - this is the realm that is returned by the server in the
      response to the initial request from the UA.

   o  nonce - this is the nonce that is returned by the server in the
      response to the initial request from the UA.

   When the server receives the request with the credentials, the server
   will verify the digest provided by the UA; if that is successful, the
   server will accept the registration and include the details of the
   token in the response.

   [[OPEN ISSUE]] How should the tokens be transported to the UA? in the
   body of the 200 OK? or a SIP header?

   The server then generates a master-key following the same procedure
   followed by the client.

   As a result of this procedure both the UA and the server would have
   created the same master-key without sending the master-key on the
   wire.

5.3.  Discarding Credentials

   After successfully receiving the access and refresh tokens from the
   proxy, the UA SHOULD discard the user credentials.

5.4.  Token Refresh

   The UA makes a refresh request to the token by sending a refresh
   REGISTER request that includes the authorization header and a body
   with the grant_type, the refresh_token, and the proof-of-possession
   of the master-key.

   For example:

      grant_type=refresh_token&refresh_token=<refresh_token>&pop=<pop>

5.5.  Authenticated Requests

   When the UA wants to send any request to the proxy, it MUST include
   the Authorization header and use the Bearer scheme to carry the
   access token, and the proof-of-possession of the master-key.

   For example:

      Authorization: Bearer token=<token>, pop=<pop>





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   See rfc4474, section 9, for the SIP headers to hash to create the
   value for the proof.

   [[OPEN ISSUE]] The Bearer scheme is used to deliver tokens without
   providing any proof of possession.  We probably need to use different
   scheme later on.

5.6.  Examples


      REGISTER sip:registrar.biloxi.com SIP/2.0
      Via: SIP/2.0/TCP bobspc.biloxi.com:5060;branch=z9hG4bKnashds7
      Max-Forwards: 70
      To: Bob <sip:bob@biloxi.com>
      From: Bob <sip:bob@biloxi.com>;tag=456248
      Call-ID: 843817637684230@998sdasdh09
      CSeq: 1826 REGISTER
      Contact: <sip:bob@192.0.2.4>
      Expires: 7200
      Content-Length: 19

      grant_type=password&pop=<pop>


      SIP/2.0 200 OK
      Via: SIP/2.0/TCP bobspc.biloxi.com:5060;branch=z9hG4bKnashds7
           ;received=192.0.2.4
      To: Bob <sip:bob@biloxi.com>;tag=2493k59kd
      From: Bob <sip:bob@biloxi.com>;tag=456248
      Call-ID: 843817637684230@998sdasdh09
      CSeq: 1826 REGISTER
      Contact: <sip:bob@192.0.2.4>
      Expires: 7200
      Content-Length: 0

      {
         "access_token":"2YotnFZFEjr1zCsicMWpAA",
         "token_type":"example",
         "expires_in":3600,
         "refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
         "example_parameter":"example_value"
      }









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6.  Outbound

   RFC5626 defines a mechanism that allows a UA to simultaneously
   connect and establish registration with multiple outbound proxies to
   get service.

   This section describes that impact of outbound on this authorization
   mechanism.

6.1.  Authorization Code Grant type

   During initial registration with the primary proxy, the UA is able to
   get an authorization code that it will use to register with the
   primary proxy.  Assuming the authorization server is shared between
   the various outbound proxies, the UA will be able to use the same
   authorization code to register with the secondary proxies and as a
   result each one of the secondary proxies will get the master-key
   associated with the user to be used for the calculation of the proof-
   of-possession.

6.2.  Resource Owner Password Credentials Grant type

   During registration the proxy challenges the UA, and both the proxy
   and the UA create a master-key based on HA1, realm, and nonce.  Since
   the nonce is not shared between the various proxies, it is not
   possible for the outbound proxies to use the same master-key; as a
   result, the UA is expected to maintain a master-key and token per
   outbound proxy.

7.  Security Considerations

      <Security considerations text>

8.  IANA Considerations

      <IANA considerations text>

9.  Acknowledgments

      <Acknowledgments text>

10.  Normative References

   [OPENID]   Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0", February 2014.

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



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   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, H., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework",
              RFC 6749, October 2012.

   [RFC7662]  Richer, J., "OAuth 2.0 Token Introspection", RFC 7662,
              October 2015.

Authors' Addresses

   Rifaat Shekh-Yusef (editor)
   Avaya
   250 Sidney Street
   Belleville, Ontario
   Canada

   Phone: +1-613-967-5267
   EMail: rifaat.ietf@gmail.com


   Victor Pascual
   Oracle
   Spain

   EMail: victor.pascual.avila@oracle.com


   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: christer.holmberg@ericsson.com














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