| SIP Core | R. Shekh-Yusef, Ed. |
| Internet-Draft | Avaya |
| Updates: 3261 (if approved) | C. Holmberg |
| Intended status: Standards Track | Ericsson |
| Expires: March 30, 2018 | V. Pascual |
| webrtchacks | |
| September 26, 2017 |
Third-Party Authentication for Session Initiation Protocol (SIP)
draft-ietf-sipcore-sip-authn-01
This document defines an authentication 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 to a dedicated third-party IdP entity that is separate from the SIP network elements that provide the SIP service.
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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 IdP entity, as well as to obtain basic profile information about the user.
This document defines an authentication 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 to a dedicated third-party IdP 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].
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.
[RFC6749] defines two types of clients, confidential and public, that apply to the SIP User Agents.
There are two types of user authentications in SIP:
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].
Authorization Code Flow is used by the SIP UA to authenticate to a third-party IdP entity to obtain an authorization code that would be later used by the SIP Proxy to obtain tokens to allow the SIP UA to register and get service from the SIP network.
The following figure provides a high level view of flow of messages for the user authentication using a Public UA that has a rich UI that would prompt the user for his credentials:
User Proxy Authorization Agent Server --------------------------------------------------------------------- | | | | F1 REGISTER | | |------------------------------>| | | F2 401 Unauthorized | | |<------------------------------| | | | | | | | The UA prompts the user to provide his/her credentials. | The UA then, as per OAuth 2.0 protocol, authenticates the user to | the AuthZ server, and obtains an authorization code, which the UA | will later hand to the Proxy. | |<------------------------------------------------------------->| | | | | | | | F3 REGISTER [authz code] | | |------------------------------>| | | | | | | The proxy will then use the | | | authz code to obtain tokens | | | from the authz server | | |<----------------------------->| | | | | F4 200 OK | | |<------------------------------| | | | | Both the proxy and the UA will then create a shared-key based on | the from-tag, to-tag, and call-id are taken from the 200 OK | | | |
The UA initially sends a REGISTER request (F1) without providing any credentials. The proxy redirects the UA by responding with 401 Unauthorized (F2).
The UA will then contact the Authorization Server and obtain an authorization code to be used with the SIP proxy.
The UA then retries the request (F3) and includes the authorization code in the body of the request.
The proxy then contacts the Authorization Server and exchanges the authorization code for tokens. If the proxy is successful in exchanging the authorization code with the tokens, the proxy then replies with 200 OK to complete the registration process, and locally generates the shared-key with the UA for this user.
When the UA receives the 200 OK, it will follow the same procedure used by the proxy and calculate its shared-key locally.
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 Unauthorized (F2) that includes the address of the Authorization Server in the form of an HTTP URI in a Location header field, as defined in RFC7231, section 7.1.2.
[[OPEN ISSUE]] The above text suggests defining a new Location header to carry the authorization server URL. Is that reasonable? other ideas?
The UA will then contact the Authorization Server and obtain an authorization code to be used with the SIP proxy. The method used by the UA to obtain the code is out of scope for this document.
The UA will then send a new REGISTER request (F3) and include the authorization code in the body of the request with the following parameters:
grant_type (REQUIRED)
code (REQUIRED)
The proxy then contacts the Authorization Server and exchanges the authorization code for access token, refresh token, and maybe ID token. The method used by the UA to obtain the tokens is out of scope for this document.
If the proxy is successful in exchanging the authorization code with the tokens, the proxy then responds with 200 OK (F4) to the UA to complete the registration process.
After sending the 200 OK to the UA to complete the registration process, the proxy and the UA use the HMAC-SHA256(key, message) to calculates the shared-key associated with this user as follows:
key
message
This shared-key will be used to allow the UA to re-register to the proxy, in case of a connection loss to the proxy, without the need to obtain a new code or prompt the user for his credentials.
When the UA loses its connection to the proxy and it wants to send a new registration request to the proxy, the UA will send a new REGISTER request and include the proof-of-possession (pop) of the shared-key in the body of the request:
grant_type (REQUIRED)
pop (REQUIRED)
The pop is calculated using the shared-key as follows:
See rfc4474, section 9, for the SIP headers to hash to create digest-string.
[[OPEN ISSUE]] Is there any issue with using digest-string as defined in RFC4474?
[[OPEN ISSUE]] Should pop not be limited to re-registration, and instead be used with all subsequent requests? If the answer is yes, a new header should be defined to carry the pop instead of carrying it in the payload.
Before the tokens expire, the proxy makes a refresh request to the Authorization Server to try to obtain new tokens. The method used by the UA to refresh the tokens is out of scope for this document.
If the proxy fails to refresh the tokens, then it MUST challenge the next request from the UA, and as a result the UA MUST go through the authorization process again.
The following figure provides a high level view of flow of messages for the user authentication using a Public UA that has a limited UI that cannot prompt the user for his credentials.
This use case requires the user to use his browser to authenticate to the Authorization Server and obtain a short lived numeric authorization code that would be used by the phone to register with the SIP proxy.
User Proxy Authorization Agent Server --------------------------------------------------------------------- | | | The UA collects the numeric code from the user through the key-pad| | | | | | | | F1 REGISTER [code] | | |------------------------------>| | | | | | | The proxy will then use the | | | authz code to obtain an access| | | token and refresh token | | |<----------------------------->| | | | | F2 200 OK | | |<------------------------------| | | | |
The UA will send a REGISTER request (F1) and include the code in the body of the request with the following parameters:
grant_type (REQUIRED)
code (REQUIRED)
The proxy then contacts the Authorization Server and exchanges the authorization code for access token, refresh token, and maybe an ID token. The method used by the UA to obtain the tokens is out of scope for this document.
If the proxy is successful in exchanging the authorization code with the tokens, the proxy then responds with 200 OK (F2) to the UA to complete the registration process.
After sending the 200 OK to the UA to complete the registration process, the proxy and the UA use the HMAC-SHA256(key, message) to calculates the shared-key associated with this user as follows:
key
message
This shared-key will be used to allow the UA to re-register to the proxy, in case of a connection loss to the proxy, without the need to obtain a new authorization code.
Before the tokens expire, the proxy makes a refresh request to the Authorization Server to try to obtain new tokens. The method used by the UA to refresh the tokens is out of scope for this document.
If the proxy fails to refresh the tokens, then it MUST challenge the next request from the UA, and as a result the UA MUST go through the authorization process again.
When the UA loses its connection to the proxy and it wants to send a new registration request to the proxy, the UA will send a new REGISTER request and include the proof-of-possession (pop) of the shared-key in the body of the request:
grant_type (REQUIRED)
pop (REQUIRED)
The pop is calculated using the shared-key as follows:
See rfc4474, section 9, for the SIP headers to hash to create digest-string.
[[OPEN ISSUE]] Should this be not limited to re-registration, and instead be used with all subsequent requests?
The resource owner password credentials flow is used by a Confidential UA with rich UI to authenticate to a third-party IdP entity and to directly obtain tokens to be able to register and get service from the SIP network.
The following figure provides a high level view of flow of messages for the OAuth Resource Owner Password Credentials flow:
User Proxy Authorization Agent Server --------------------------------------------------------------------- | | | The UA contacts the authorization server and authenticates the | user, and as a result obtains an access and refresh tokens. | | | | |<------------------------------------------------------------->| | | | | | | | F1 REGISTER Authorization: Bearer access_token=<access_token> | |------------------------------>| | | | | | | The proxy validates the token | | | Optional introspection step | | |<----------------------------->| | | | | F2 200 OK | | |<------------------------------| | | | |
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 method used by the UA to obtain the tokens is out of scope for this document.
The UA starts the registration process with the SIP proxy by sending a REGISTER request (F1) with the access token it obtained previously.
The UA includes an Authorization header field with the Bearer scheme in the request to carry the access token obtained previously.
The proxy then validates the token, and MAY perform an introspection step to get more information about the token and its scope. The introspection step is out of scope for this document.
When the proxy is satisfied with the token, it then replies with the 200 OK to complete the registration process.
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.
Authorization = "Authorization" HCOLON "Bearer" LWS
"access_token" EQUAL access_token
access_token = quoted-string
This section describes the syntax of the authorization header with the Bearer scheme.
<Security considerations text>
<IANA considerations text>
<Acknowledgments text>
| [MITKB] | , MIT., "IdP (Identity Provider)", MIT Knowledge Base, http://kb.mit.edu/confluence/x/XoK2, March 2011. |
| [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. |
| [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. |