SIP Core                                                  R. Shekh-Yusef, Ed. Shekh-Yusef
Internet-Draft                                                     Avaya
Updates: 3261 (if approved)                                  C. Holmberg
Intended status: Standards Track                                Ericsson
Expires: January 8, April 14, 2020                                       V. Pascual
                                                             webrtchacks
                                                            July 7,
                                                        October 12, 2019

  Third-Party Token-based Authentication and Authorization for Session
                       Initiation Protocol (SIP)
                 draft-ietf-sipcore-sip-token-authnz-02
                 draft-ietf-sipcore-sip-token-authnz-03

Abstract

   This document defines a mechanism for SIP, that is based on the OAuth
   2.0 and OpenID Connect Core 1.0 specifications, to enable the
   delegation of the user authentication and SIP registration
   authorization to a dedicated third-party entity that is separate from
   the SIP network elements that provide the SIP service.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  SIP User Agent Types  . . . . . . . . . . . . . . . . . .   3
   2.  Authentication and Authorization flow  SIP Procedures  . . . . . . . . . . . . . . . . .   4
     2.1.  Overview . . . . . .   4
     2.1.  UAC Behavior  . . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Configured AS  Obtaining Tokens  . . . . . . . . . . . . . . . . . .   4
       2.1.2.  Protecting the Access Token . . . . . . . . . . . . .   4
       2.1.2.  Discovered AS
       2.1.3.  REGISTER Request  . . . . . . . . . . . . . . . . . .   5
       2.1.4.  Non-REGISTER Request  . .   6
     2.2.  Initial Registration . . . . . . . . . . . . . .   5
     2.2.  UAS and Registrar Behavior  . . . .   7
     2.3.  Subsequent Registrations . . . . . . . . . . .   6
     2.3.  Proxy Behavior  . . . . .   8
     2.4.  Non-Registration Requests . . . . . . . . . . . . . . . .   8   6
   3.  WWW-Authenticate Response Header Field  . . . . . . . . . . .   8   6
   4.  'sip.token' Media Feature Tag . . . . . . . . . . . . . . . .   9   7
   5.  Example Flows . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Registration  . . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Registration with Pre-Configured AS . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  12
     7.1.  SIP Media Feaure Tag  . . . . . . . . . . . . . . . . . .  10
       6.1.1.  12
       7.1.1.  sip.token . . . . . . . . . . . . . . . . . . . . . .  10
   7.  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  12
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  11  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12  14

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.

   OAuth 2.0 [RFC6749] defines a token based authorization framework to
   allow clients to access resources on behalf of their user.

   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 user based on the
   authentication performed by a dedicated authorization server, as well
   as to obtain basic profile information about the user.

   This document defines an mechanism for SIP, that is based on the
   OAuth 2.0 and OpenID Connect Core 1.0 specifications, to enable the
   delegation of the user authentication and SIP registration
   authorization to a dedicated third-party entity that is separate from
   the SIP network elements that provide the SIP service.

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.  SIP User Agent Types

   [RFC6749] defines two types of clients, confidential and public, that
   apply to the SIP User Agents.

   o  Confidential User Agent: is a SIP UA that is capable of
      maintaining the confidentiality of the user credentials and any
      tokens obtained using these user credentials.

   o  Public User Agent: is a SIP UA that is incapable of maintainings
      the confidentiality of the user credentials and any obtained
      tokens.

2.  Authentication and Authorization flow

   This flow is used by  SIP Procedures

   Section 22 of [RFC3261] defines the SIP procedures for the Digest
   authentication mechanism procedures.  The same procedures apply to
   the Bearer authentication mechanism, with the changes described in
   this section.

2.1.  UAC Behavior

2.1.1.  Obtaining Tokens

   When a Confidential UA UAC sends a request without credentials (or with rich UI to authenticate credentials
   that are no longer valid), and receives a 401 (Unauthorized) or a 407
   (Proxy Authentication Required) response that contains a WWW-
   Authenticate header field (in case of a 401 response) or a Proxy-
   Authenticate header field (in case of a 407 response) that indicates
   "Bearer" scheme authentication and contains an address to an authorization server and
   Authorization Server, the UAC contacts the Authorization Server in
   order to directly obtain tokens.  The tokens returned to be able
   to register and get service from the SIP network.

2.1.  Overview

   The following sections provide overview of UA depend on the supported flows.

2.1.1.  Configured AS

   The following figure provides a high level view of flow of messages
   when the UA is aware of the AS ahead of time:

     UA                          Registrar                          AS
   ---------------------------------------------------------------------
     |                               |                               |
   [00] The UA prompts the user to provides his credentials          |
     |                               |                               |
     | [01] HTTP POST /token         |                               |
     |-------------------------------------------------------------->|
     |                               |                               |
     |         [02] 200 OK {access_token, refresh_token, [id_token]} |
     |<--------------------------------------------------------------|
     |                               |                               |
     |                               |                               |
     | [03] REGISTER                 |                               |
     |      Authorization: Bearer <access_token>                     |
     |------------------------------>|                               |
     |                               |                               |
     |                               |    [04] HTTP POST /introspect |
     |                               |           {access_token}      |
     |                               |------------------------------>|
     |                               |                               |
     |                               |        [05] 200 OK {metadata} |
     |                               |<------------------------------|
     |                               |                               |
     |                   [06] 200 OK |                               |
     |<------------------------------|                               |
     |                               |                               |

   In step [00], the UA collects the user's credentials with the AS.

   In steps [01] and [02], the UA first contacts the Authorization
   Server to authenticate the user and obtain tokens to be used to get
   access to the SIP network.

   The tokens returned to the UA depend on the type
   type of server: with an OAuth Authorization Server, AS, the tokens provided are the access
   token and refresh token.  With an OpenID Connect server, an
   additional ID-
   Token ID-Token is returned, which contains the SIP URI of the user. and other
   user specific details.  The method used to authenticate the user and
   obtain these tokens is out of scope for this document.

   In step [03], the UA starts the registration process with the SIP
   registrar by sending a REGISTER request document, with one
   potential method is the access token it
   obtained previously. Native App mechanism defined in [RFC8252].

   NOTE: The registrar validates address of the access token, and if Authorization Server might be known to the access token
   provided by
   UAC e.g., using means of configuration, in which case the UA is an opaque token, then UAC can
   contact the registrar MAY perform
   an introspection, steps [04] and [05], Authorization Server in order to obtain more information
   about the token and its scope, as per [RFC7662].  Otherwise, after
   the registrar validates the access token to make sure it was signed by a
   trusted entity,
   before it inspects its claims and act upon it.

   When the registrar is satisfied with sends SIP request without credentials.

2.1.2.  Protecting the token, it then replies Access Token

   [RFC6749] mandates that Access Tokens are protected with
   the 200 OK TLS when in
   transit.  However, TLS only guarantees hop-to-hop protection when
   used to complete protect SIP signaling.  Therefore the registration process.

2.1.2.  Discovered AS

   The following figure provides Access Token MUST be
   protected in a high level view of flow of messages way so that only authorized SIP servers will have
   access to it.  Endpoints that support this specifications MUST
   support encrypted JSON Web Tokens (JWT) [RFC7519] for encoding and
   protecting Access Token when the UA discovers the AS included in SIP requests, unless some
   other mechanism is used to guarantee that only authorized SIP
   endpoints have access to conatc from the registrar:

     UA                          Registrar                          AS
   ---------------------------------------------------------------------
     |                               |                               |
     | [07] Access Token.

2.1.3.  REGISTER                 |                               |
     |------------------------------>|                               |
     |                               |                               |
     | [08] 401 Unauthorized         |                               |
     |      WWW-Authenticate: Bearer "authz_server"="<authz_server>" |
     |<------------------------------|                               |
     |                               |                               |
   [09] Request

   The UA prompts the user to provides his credentials          |
     |                               |                               |
     | [10] HTTP POST /token         |                               |
     |-------------------------------------------------------------->|
     |                               |                               |
     |         [11] 200 OK {access_token, refresh_token, [id_token]} |
     |<--------------------------------------------------------------|
     |                               |                               |
     | [12] REGISTER                 |                               |
     |      Authorization: Bearer <access_token>                     |
     |------------------------------>|                               |
     |                               |    [13] HTTP POST /introspect |
     |                               |           {access_token}      |
     |                               |------------------------------>|
     |                               |                               |
     |                               |        [14] 200 OK {metadata} |
     |                               |<------------------------------|
     |                               |                               |
     |                   [15] 200 OK |                               |
     |<------------------------------|                               |
     |                               |                               |

   In step [07] the UA starts procedures in this section assumes that the registration process by sending UAC has obtained a
   token as specified in section Section 2.1.1

   When a UAC sends a SIP REGISTER request in order to the registrar without any credentials.  The
   REGISTER request includes create a binding, it
   MUST include an indication that Authorization headerf field with a Bearer scheme,
   carrying the UA supports token-
   based autentication access token, in the form of sip.token media feature tag.  The
   registrar then challenges the UA, request, as specified in step [08], by responding with
   401 Unauthorized and includes the authorization server to contact to
   obtain a token.

   In step [09], the UA collects [RFC6750].
   Based on local policy, the user's credentials UAC MAY include an access token that has
   been used for another binding associated with the AS.

   In steps [10] and [11], same AOR in the UA contacts
   request.

   When the UAC sends a binding refresh REGISTER request, it SHOULD
   include an Authorization Server to
   authenticate header field with either the user and obtain tokens to be access token
   previously used to get for the binding, or a new access to token (obtained
   using the SIP network. refresh token) if the previous one has expired.

   If the access token included in a REGISTER request is not accepted,
   and the UAC receives a 401 response or a 407 response, the UAC
   follows the procedures in Section 2.1.1.

2.1.4.  Non-REGISTER Request

   The tokens returned to procedures in this section assumes that the UA depend on UAC has obtained a
   token as specified in section Section 2.1.1

   When a UAC sends a request in order to initiate a SIP dialog, or
   sends a stand-alone request, the type of server: with UAC MUST include an
   OAuth Authorization Server, the tokens provided are
   header field with a Bearer scheme, carrying the access token
   and refresh token.  With an OpenID Connect server, an additional ID-
   Token is returned, which contains token, in the SIP URI of
   request, as specified in [RFC6750].  Based on local policy, the user.  The
   method UAC
   MAY include an access token that has been used to authenticate for another dialog, or
   for another stand-alone request, if the user and obtain these tokens is out target of scope for this document.

   In step [12], the UA retries new request is
   the registration process with same.

   When the SIP
   registrar by sending UAC sends a REGISTER request mid-dialog request, the UAC SHOULD include an
   Authorization header field with either the access token it
   obtained previously.

   The registrar validates previously
   used within the dialog, or with a new access token, and token if the access token
   provided by previous
   one has expired or the UA is an opaque token, then then registrar MAY
   perform an introspection, steps [13] and [14], to obtain more
   information about UAC refreshed the access token and before its scope, as per [RFC7662].
   Otherwise, after the registrar validates
   expiry time.

   If the access token to make sure it
   was signed by included in a trusted entity, it inspects its claims request is not accepted, and act upon
   it.

2.2.  Initial Registration

   If the UA has already obtained
   UAC receives a token, then 401 response or a 407 response, the UA starts UAC follows the
   registration process, step [03], by sending
   procedures in Section 2.1.1.

2.2.  UAS and Registrar Behavior

   When a REGISTER request, UAS or a Registrar receives a SIP request that does not
   contain an Authorization header field with
   the a valid access token in token, and
   the Authorization header, UAS/Proxy decides to challenge the registrar.

   If the UA does not have a token, then originator of the UA starts request, the registration
   process, step [07], by sending a REGISTER request without an
   Authorization header.  The registrar
   proxy MUST then challenge the UA by
   responding with 401 Unauthorized request and include the WWW-Authenticate
   Response Header Field which includes the server to contact to obtain send a token, as specified in Section 3 401 (Unauthorized)
   response.  The REGISTER request SHOULD UAS/Proxy MUST include a sip.token media feature tag in
   the Contact Proxy-Authentication header
   field of the request, unless it knows (e.g., by
   means of configuration) that the registrar supports in the token
   authentication mechanism.

   The UA MUST response, indicate "Bearer" scheme and include an
   address to an Authorization Server from there the originator can
   obtain an access token.

   When a UAS/Registrar receives a SIP request that contains an
   Authorization header field with an access token, the Bearer
   scheme in the request to carry UAS/Registrar
   MUST validate the access token, as specified in
   [RFC6750].

   When using the registrar is satisfied procedures associated with
   the token, it then replies with type of access token used.  If the 200 OK validation is successful the
   UAS/Registrar can continue to complete process the registration process.

2.3.  Subsequent Registrations

   All subsequent REGISTER requests from request using normal SIP
   procedures.  If the UA validation fails, the UAS/Registrar 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 reject
   the
   system.  The method used to obtain request.

2.3.  Proxy Behavior

   When a new fresh access tokens is out
   of scope for this document.

   The REGISTER proxy receives a SIP request SHOULD include that does not contain a sip.token media feature tag in
   the Contact Proxy-
   Authorization header field of with a valid access token, and the request, unless it knows (e.g., by
   means proxy
   decides to challenge the originator of configuration) that the registrar supports request, the token
   authentication mechanism.

2.4.  Non-Registration Requests

   The UA proxy MUST NOT insert a token in a non-REGISTER request, unless
   challenge the
   non-REGISTER request has been challenged, or the peer is considered a
   trusted entity.

   If and send a non-REGISTER request from the UA is challenged with 407 (Proxy Authentication Required)
   response.  The proxy MUST include a WWW-
   Authenticate Proxy-Authentication header field to provide credentials for the same realm
   specified
   in the challenge response, indicate "Bearer" scheme and include an address to
   an Authorization Server from there the registration request, then the UA
   MUST include a valid originator can obtain an
   access token in the token.

   When a proxy receives a SIP request retry.  The UA MUST
   include that contains an Proxy-
   Authorization header field with an access token, and the Bearer scheme in proxy has
   previously challenged the
   request to carry originator of the request, the proxy MUST
   validate the access token, as specified in [RFC6750].

   Challenges with WWW-Authenticate using the procedures associated with different realm specified in the challenge
   type of access token used.  If the validation is successful the proxy
   can continue to process the registration request are out of scope for this
   document.  Challenges with Proxy-Authenticate are out of scope for
   this document. using normal SIP procedure.  If
   the validation fails, the UAS/Registrar MUST reject the request.

3.  WWW-Authenticate Response Header Field

   This section describes the syntax of the WWW-Authenticate Response
   Header Field when used with the Bearer scheme to challenge the UA for
   credentials.

       challenge  =/  ("Bearer" LWS bearer-cln *(COMMA bearer-cln))
       bearer-cln = realm / scope / authz-server / error /
                    auth-param
       authz-server = "authz_server" EQUAL authz-server-value
       authz-server-value = quoted-string

   The realm and auth-param parameters are defined in [RFC3261].

   As per [RFC3261], the realm string alone defines realm string alone defines the protection
   domain.  [RFC3261] states that the realm string must be globally
   unique and recommends that the realm string contains a hostname or
   domain name.  It also states that the realm string should be human-
   readable identifier that can be rendered to the user.

   The scope and error parameters are defined in [RFC6749].

   The scope parameter could be used by the registrar/proxy to indicate
   to the UAC the minimum scope that must be associated with the access
   token to be able to get service.  As defined in [RFC6749], the value
   of the scope parameter is expressed as a list of space-delimited,
   case-sensitive strings.  The strings are defined by the authorization
   server.  The values of the scope parameter is out of scope for this
   document.

   The error parameter could be used by the registrar/proxy to indicate
   to the UAC the reason for the error, with possible values of
   "invalid_token" or "invalid_scope".

4.  'sip.token' Media Feature Tag

   The sip.token media feature tag, when inserted in the Contact header
   field of a SIP REGISTER request, conveys that the SIP UA associated
   with the tag supports a token based authentication mechanism, where
   the user authentication and SIP registration authorization is
   performed by a third party.  The media feature tag has no values.

   token-mt = "+sip.token"

5.  Example Flows

5.1.  Registration

   The figure belows show an example of a SIP registration, where the UA
   is informed about the Authorization Server (AS) from where to obtain
   an access token by the registratar in a 401 response to the REGISTER
   request.

     UA                          Registrar                          AS
   ---------------------------------------------------------------------
     |                               |                               |
     | [1] REGISTER                  |                               |
     |------------------------------>|                               |
     |                               |                               |
     | [2] 401 Unauthorized          |                               |
     |     WWW-Authenticate: Bearer "authz_server"="<authz_server>"  |
     |<------------------------------|                               |
     |                               |                               |
     | [3] The UA colects the user AS credentials                    |
     |                               |                               |
     | [4] HTTP POST /token          |                               |
     |- - - - - - - - - -  - - - - - - - - - - - - - - - - - - - - ->|
     |                               |                               |
     | [5] 200 OK {access_token, refresh_token, [id_token]}          |
     |<- - - - - - - - - -  - - - - - - - - - - - - - - - - - - - - -|
     |                               |                               |
     | [6] REGISTER                  |                               |
     |     Authorization: Bearer <access_token>                      |
     |------------------------------>|                               |
     |                               | [7] HTTP POST /introspect     |
     |                               |     {access_token}            |
     |                               |------------------------------>|
     |                               |                               |
     |                               | [8] 200 OK {metadata}         |
     |                               |<------------------------------|
     |                               |                               |
     | [9] 200 OK                    |                               |
     |<------------------------------|                               |
     |                               |                               |

   In step [1], the UA starts the registration process by sending a SIP
   REGISTER request to the registrar without any credentials.  The
   REGISTER request includes an indication that the UA supports token-
   based autentication, using a sip.token media feature tag.

   In step [2], the registrar challenges the UA, by sending a SIP 401
   (Unauthorized) response to the REGISTER request.  In the response the
   registrar includes information about the AS to contact in order to
   obtain a token.

   In step [3], the UA collects the user credentials associated with the
   AS.

   In steps [4] and [5], the UA contacts the AS in order to authenticate
   the user and to obtain tokens to be used to get access to the SIP
   network.

   The tokens returned to the UA depend on the type of server: with an
   OAuth AS, the tokens provided are the access token and refresh token.
   With an OpenID Connect server, an additional ID-Token is returned,
   which contains the SIP URI of the user.  The method used to
   authenticate the user and obtain these tokens is out of scope for
   this document.

   In step [6], the UA retries the registration process by sending a new
   SIP REGISTER request that includes the access token that the UA
   obtrained in steps [10] and [11].

   The registrar validates the access token.  If the access token is a
   reference token, the registrar MAY perform an introspection, as in
   steps [7] and [8], in order to obtain more information about the
   access token and its scope, as per [RFC7662].  Otherwise, after the
   registrar validates the token to make sure it was signed by a trusted
   entity, it inspects its claims and act upon it.

   In step [9], once the registrar has succesfully verified and accepted
   the access token, it sends a 200 (OK) response to the REGISTER
   request.

5.2.  Registration with Pre-Configured AS

   The figure belows show an example of a SIP registration, where the UA
   is has pre-configured information about the Authorization Server (AS)
   from where to obtain the access token.

     UA                          Registrar                          AS
   ---------------------------------------------------------------------
     |                               |                               |
     | [1] The UA collects the user AS credentials                   |
     |                               |                               |
     | [2] HTTP POST /token          |                               |
     |- - - - - - - - - -  - - - - - - - - - - - - - - - - - - - - ->|
     |                               |                               |
     | [3] 200 OK {access_token, refresh_token, [id_token]}          |
     |<- - - - - - - - - -  - - - - - - - - - - - - - - - - - - - - -|
     |                               |                               |
     |                               |                               |
     | [4] REGISTER                  |                               |
     |     Authorization: Bearer <access_token>                      |
     |------------------------------>|                               |
     |                               | [5] HTTP POST /introspect     |
     |                               |     {access_token}            |
     |                               |------------------------------>|
     |                               |                               |
     |                               | [6] 200 OK {metadata}         |
     |                               |<------------------------------|
     |                               |                               |
     | [7] 200 OK                    |                               |
     |<------------------------------|                               |
     |                               |                               |

   In step [1], the UA collects the protection
   domain.  [RFC3261] states that user credentials associated with the realm string must be globally
   unique
   AS.

   In steps [2] and recommends that [3], the realm string contains a hostname or
   domain name.  It also states that UA contacts the realm string should be human-
   readable identifier that can be rendered AS in order to authenticate
   the user.

   The scope user and error parameters are defined in [RFC6749].

   The scope parameter could be used by the registrar/proxy to indicate to the UAC the minimum scope that must be associated with the access
   token obtain tokens to be able used to get service.  As defined in [RFC6749], the value
   of the scope parameter is expressed as a list of space-delimited,
   case-sensitive strings.  The strings are defined by the authorization
   server.  The values of access to the scope parameter is out of scope for this
   document. SIP
   network.

   The error parameter could be used by the registrar/proxy to indicate tokens returned to the UAC the reason for the error, with possible values of
   "invalid_token" or "invalid_scope".

4.  'sip.token' Media Feature Tag

   The sip.token media feature tag, when inserted in UA depend on the Contact header
   field type of a SIP REGISTER request, conveys that the SIP UA associated server: with an
   OAuth AS, the tag supports a token based authentication mechanism, where tokens provided are the user authentication access token and SIP registration authorization is
   performed by a third party.  The media feature tag has no values.

   token-mt = "+sip.token"

5.  Security Considerations

   The UAC MUST always make sure that it refresh token.
   With an OpenID Connect server, an additional ID-Token is communicating with returned,
   which contains the right
   registrar/proxy using TLS and proper validation SIP URI of the server
   certificate user.  The method used to
   authenticate the user and obtain these tokens is out of scope for
   this document.

   In step [4], the identifier in UA retries the registration process by sending a new
   SIP REGISTER request that certificate to protect includes the access token that the UA
   obtrained in transit. steps [10] and [11].

   The registrar validates the access token.  If the access token being used is a bearer token
   reference token, the registrar MAY perform an introspection, as specified in [RFC6750],
   then
   steps [5] and [6], in order to obtain more information about the security considration of that document apply.

   If
   access token and its scope, as per [RFC7662].  Otherwise, after the
   registrar validates the token being used is to make sure it was signed by a JWT as specified in [RFC7519], then trusted
   entity, it inspects its claims and act upon it.

   In step [7], once the registrar has succesfully verified and accepted
   the access token, it sends a 200 (OK) response to the REGISTER
   request.

6.  Security Considerations

   The security considerations for OAuth are defined in [RFC6749].  The
   security considerations for bearer tokens are defined in [RFC6750].
   The security considerations for JSON Web Tokens (JWT) are defined in
   [RFC7519].  These security considration considerations also apply to SIP usage of
   access token as defined in this document.

   [RFC6749] mandates that document apply.

6. Access Tokens are protected with TLS.
   However, TLS only guarantees hop-to-hop protection when used to
   protect SIP signaling.  Therefore the Access Token MUST be protected
   in a way so that only authorized SIP endpoints will have access to
   it.  Endpoints that support this specifications MUST support
   encrypted JSON Web Tokens (JWT) [RFC7519] for encoding and protecting
   Access Token when included in SIP requests, unless some other
   mechanism is used to guarantee that only authorized SIP endpoints
   have access to the Access Token.

7.  IANA Considerations

6.1.

7.1.  SIP Media Feaure Tag

6.1.1.

7.1.1.  sip.token

   This section defines a new media feature tag that extends the "SIP
   Media Feature Tag Registration Tree" subregistry [RFC3840] under the
   "Media Feature Tags" registry (https://www.iana.org/assignments/
   media-feature-tags).

    Media feature tag name: sip.token

    Summary of the media feature indicated by this feature tag: This
        media feature tag, when inserted in the Contact header field
        of a SIP REGISTER request, conveys that the SIP UA associated
        with the tag supports a token based authentication mechanism,
        where the user authentication and SIP registration authorization
        is performed by a third party.

     Values appropriate for use with this feature tag: none

     Related standards or documents: RFC XXXX

     Security considerations: This media feature tag does not introduce
        new security considerations, as it simply indicates support for
        a basic SIP feature. However, if an attacker manages to remove
        the media feature tag from a SIP REGISTER request, the SIP UA
        that inserted it might not be able to authenticate itself with
        the SIP registrar to which the SIP request is addressed, as the
        SIP registrar might not be aware that the SIP UA supports the
        feature associated with the media feature tag.

     Contact: IESG (iesg@ietf.org)

7.

8.  Acknowledgments

   The authors would also like to thank Paul Kyzivat the following for his reviews their review
   and feedback on this document. document:

   Paul Kyzivat, Olle Johansson, Roman Shpount, and Dale Worley.

   The authors would also like to thank the following for their review
   and feedback of the original document that was replaced with this
   document:

   Andrew Allen, Martin Dolly, Keith Drage, Paul Kyzivat, Jon Peterson,
   Michael Procter, Roy Radhika, Matt Ryan, Ivo Sedlacek, Roman Shpount,
   Robert Sparks, Asveren Tolga, and Dale Worley.

8.

9.  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,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
              "Indicating User Agent Capabilities in the Session
              Initiation Protocol (SIP)", RFC 3840,
              DOI 10.17487/RFC3840, August 2004,
              <https://www.rfc-editor.org/info/rfc3840>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC7523]  Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
              (JWT) Profile for OAuth 2.0 Client Authentication and
              Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
              2015, <https://www.rfc-editor.org/info/rfc7523>.

   [RFC7662]  Richer, J., Ed., "OAuth 2.0 Token Introspection",
              RFC 7662, DOI 10.17487/RFC7662, October 2015,
              <https://www.rfc-editor.org/info/rfc7662>.

   [RFC8252]  Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
              BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
              <https://www.rfc-editor.org/info/rfc8252>.

Authors' Addresses

   Rifaat Shekh-Yusef (editor)
   Avaya
   425 Legget Drive
   Ottawa, Ontario
   Canada

   Phone: +1-613-595-9106
   EMail: rifaat.ietf@gmail.com

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: christer.holmberg@ericsson.com

   Victor Pascual
   webrtchacks
   Spain

   EMail: victor.pascual.avila@gmail.com