| SIP Core | R. Shekh-Yusef, Ed. |
| Internet-Draft | Avaya |
| Updates: 3261 (if approved) | C. Holmberg |
| Intended status: Standards Track | Ericsson |
| Expires: January 8, 2020 | V. Pascual |
| webrtchacks | |
| July 7, 2019 |
Third-Party Token-based Authentication and Authorization for Session Initiation Protocol (SIP)
draft-ietf-sipcore-sip-token-authnz-02
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.
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This Internet-Draft will expire on January 8, 2020.
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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.
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].
[RFC6749] defines two types of clients, confidential and public, that apply to the SIP User Agents.
This flow is used by a Confidential UA with rich UI to authenticate to an authorization server and to directly obtain tokens to be able to register and get service from the SIP network.
The following sections provide overview of the supported flows.
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 of server: with an OAuth Authorization Server, 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 [03], the UA starts the registration process with the SIP registrar by sending a REGISTER request with the access token it obtained previously.
The registrar validates the access token, and if the access token provided by the UA is an opaque token, then the registrar MAY perform an introspection, steps [04] and [05], to obtain more information about the 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.
When the registrar is satisfied with the token, it then replies with the 200 OK to complete the registration process.
The following figure provides a high level view of flow of messages when the UA discovers the AS to conatc from the registrar:
UA Registrar AS
---------------------------------------------------------------------
| | |
| [07] REGISTER | |
|------------------------------>| |
| | |
| [08] 401 Unauthorized | |
| WWW-Authenticate: Bearer "authz_server"="<authz_server>" |
|<------------------------------| |
| | |
[09] 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 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 in the form of sip.token media feature tag. The registrar then challenges the UA, 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 the user's credentials with the AS.
In steps [10] and [11], the UA 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 of server: with an OAuth Authorization Server, 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 [12], the UA retries the registration process with the SIP registrar by sending a REGISTER request with the access token it obtained previously.
The registrar validates the access token, and if the access token provided by the UA is an opaque token, then then registrar MAY perform an introspection, steps [13] and [14], to obtain more information about the 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.
If the UA has already obtained a token, then the UA starts the registration process, step [03], by sending a REGISTER request, with the access token in the Authorization header, to the registrar.
If the UA does not have a token, then the UA starts the registration process, step [07], by sending a REGISTER request without an Authorization header. The registrar MUST then challenge the UA by responding with 401 Unauthorized and include the WWW-Authenticate Response Header Field which includes the server to contact to obtain a token, as specified in Section 3
The REGISTER request SHOULD include a sip.token media feature tag in the Contact header field of the request, unless it knows (e.g., by means of configuration) that the registrar supports the token authentication mechanism.
The UA MUST include an Authorization header field with the Bearer scheme in the request to carry the access token, as specified in [RFC6750].
When the registrar is satisfied with the token, it then replies with the 200 OK to complete the registration process.
All subsequent REGISTER 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. The method used to obtain a new fresh access tokens is out of scope for this document.
The REGISTER request SHOULD include a sip.token media feature tag in the Contact header field of the request, unless it knows (e.g., by means of configuration) that the registrar supports the token authentication mechanism.
The UA MUST NOT insert a token in a non-REGISTER request, unless the non-REGISTER request has been challenged, or the peer is considered a trusted entity.
If a non-REGISTER request from the UA is challenged with a WWW-Authenticate header field to provide credentials for the same realm specified in the challenge to the registration request, then the UA MUST include a valid access token in the request retry. The UA MUST include an Authorization header field with the Bearer scheme in the request to carry the access token, as specified in [RFC6750].
Challenges with WWW-Authenticate with different realm specified in the challenge to the registration request are out of scope for this document. Challenges with Proxy-Authenticate are out of scope for this document.
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
This section describes the syntax of the WWW-Authenticate Response Header Field when used with the Bearer scheme to challenge the UA for credentials.
The realm and auth-param parameters are defined in [RFC3261].
As per [RFC3261], the 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".
token-mt = "+sip.token"
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.
The UAC MUST always make sure that it is communicating with the right registrar/proxy using TLS and proper validation of the server certificate and the identifier in that certificate to protect the access token in transit.
If the token being used is a bearer token as specified in [RFC6750], then the security considration of that document apply.
If the token being used is a JWT as specified in [RFC7519], then the security considration of that document apply.
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)
The authors would also like to thank Paul Kyzivat for his reviews and feedback on this document.
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.