SIP Core R. Shekh-Yusef
Internet-Draft Avaya
Updates: 3261 (if approved) C. Holmberg
Intended status: Standards Track Ericsson
Expires: July 18, 2020 V. Pascual
webrtchacks
January 15, 2020
Third-Party Token-based Authentication and Authorization for Session
Initiation Protocol (SIP)
draft-ietf-sipcore-sip-token-authnz-07
Abstract
This document defines a SIP mechanism that relies on the OAuth 2.0
and OpenID Connect Core 1.0 to enable delegation of the user
authentication and SIP registration authorization to a third-party.
The document updates RFC 3261.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. SIP User Agent Types . . . . . . . . . . . . . . . . . . 3
2. SIP Procedures . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. Obtaining Tokens . . . . . . . . . . . . . . . . . . 4
2.1.2. Protecting the Access Token . . . . . . . . . . . . . 5
2.1.3. REGISTER Request . . . . . . . . . . . . . . . . . . 5
2.1.4. Non-REGISTER Request . . . . . . . . . . . . . . . . 6
2.2. UAS and Registrar Behavior . . . . . . . . . . . . . . . 6
2.3. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 6
3. Access Token Claims . . . . . . . . . . . . . . . . . . . . . 7
4. WWW-Authenticate Response Header Field . . . . . . . . . . . 7
5. Example Flows . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Registration . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Registration with Pre-Configured AS . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. Normative References . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] uses the framework
used by HTTP [RFC7230] 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.
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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 updates [RFC3261], by defining the UAC procedures if it
receives a 401/407 response with multiple WWW-Authenticate/Proxy-
Authenticate header fields, providing challenges using different
authentication schemes for the same realm.
This document defines an mechanism for SIP, that relies 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 maintaining
the confidentiality of the user credentials and any obtained
tokens.
The mechanism defined in this document MUST only be used with
Confidential User Agents, as the UA is expected to obtain and
maintain tokens to be able to access the SIP network.
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2. 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 UAC sends a request without credentials (or with 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, the UAC contacts the Authorization Server in
order to obtain tokens, and includes the requested scopes, based on a
local configuration.
The tokens returned to the UA depend on the type of AS: with an OAuth
AS, the tokens provided are the access token and refresh token. The
access token will be sent to the SIP servers to authorize UAC's
access to the service. The refresh token will only be used with the
AS to get new access token and refresh token, before the expiry of
the current access token. With an OpenID Connect server, an
additional ID-Token is returned, which contains the SIP URI and other
user specific details, and will be consumed by the UAC.
The detailed OAuth2 procedure to authenticate the user and obtain
these tokens is out of scope of this document. [RFC8252] defines
procedures for native applications. When using the mechanism defined
in [RFC8252] the user will be directed to use a browser for the
interaction with the authorization server, allowing the authorization
server to prompt the user for multi-factor authentication, redirect
the user to third-party identity providers, and the use of single-
sign-on sessions.
If the UAC receives a 401/407 response with multiple WWW-
Authenticate/Proxy-Authenticate header fields, providing challenges
using different authentication schemes for the same realm, the UAC
provides credentials for one or more of the schemes that it supports,
based on local policy.
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NOTE: The address of the Authorization Server might be known to the
UAC e.g., using means of configuration, in which case the UAC can
contact the Authorization Server in order to obtain the access token
before it sends SIP request without credentials.
2.1.2. Protecting the Access Token
[RFC6749] mandates that Access Tokens are protected with TLS when in
transit. 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 servers will have
access to it. Endpoints that support this specification 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.
2.1.3. REGISTER Request
The procedures in this section assumes that the UAC has obtained a
token as specified in section Section 2.1.1
When the UAC sends a REGISTER request after it received a challenge
containing the Bearer scheme, then to resolve that particular
challenge it needs to send a request with an Authorization header
field containing the response to that challenge, including the Bearer
scheme carrying a valid access token in the request, as specified in
[RFC6750].
Note that if there were multiple challenges with different schemes
then it maybe able to successfully retry the request using non-Bearer
credentials.
Based on local policy, the UAC MAY include an access token that has
been used for another binding associated with the same AOR in the
request.
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.
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2.1.4. Non-REGISTER Request
The procedures in this section assumes that the UAC has obtained a
token as specified in section Section 2.1.1
When a UAC sends a request, after it received a challenge containing
the Bearer scheme, then the UAC MUST include an Authorization header
field with a Bearer scheme, carrying a valid access token in the
request, as specified in [RFC6750]. Based on local policy, the UAC
MAY include an access token that has been used for another dialog, or
for another stand-alone request, if the target of the new request is
the same.
If the access token included in a 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.
2.2. UAS and Registrar Behavior
When a UAS or Registrar receives a request that fails to contain
authorization credentials acceptable to it, it SHOULD challenge the
request by sending a 401 (Unauthorized) response. To indicate that
it is willing to accept an OAuth2 token as a credential the UAS/
Registrar MUST include a Proxy-Authentication header field in the
response, indicate "Bearer" scheme and include an address of an
Authorization Server from which 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 UAS/Registrar
MUST validate the access token, using the procedures associated with
the type of access token used, e.g. [RFC7519]. If the validation is
successful the UAS/Registrar can continue to process the request
using normal SIP procedures. If the validation fails, the UAS/
Registrar MUST reject the request.
2.3. Proxy Behavior
When a proxy receives a request that fails to contain authorization
credentials acceptable to it, it SHOULD challenge the request by
sending a 407 (Proxy Authentication Required) response. To indicate
that it is willing to accept an OAuth2 token as a credential the
proxy MUST include a Proxy-Authentication header field in the
response, indicating "Bearer" scheme and including an address to an
Authorization Server from which the originator can obtain an access
token.
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When a proxy wishes to authenticate a received request, it MUST
search the request for Proxy-Authorization header fields with 'realm'
parameters that match its realm. It then MUST successfully validate
the credentials from at least one Proxy-Authorization header field
for its realm. When the scheme is Bearer the proxy MUST validate the
access token, using the procedures associated with the type of access
token used, e.g. [RFC7519].
3. Access Token Claims
The type of services that an access token grants access to can be
determined using different methods. Which methods are used and the
granted access provided by the token is based on local policy agreed
between the AS and the registrar.
If an access token is encoded as a JWT, it might contain a list of
claims [RFC7519], some registered and some are application specific
claims. The REGISTRAR can grant access to services either based on
such claims, using some other mechanism, or a combination of claims
and some other mechanism. If an access token is a reference token,
the REGISTRAR will grant access based on some other mechanism.
Examples of such other mechanisms are introspection [RFC7662], user
profile lookups, etc.
4. 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, by extending the 'challnge' header field defined by
[RFC3261].
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 = https-URI
realm = <defined in RFC3261>
auth-param = <defined in RFC3261>
scope = <defined in RFC6749>
error = <defined in RFC6749>
https-URI = <defined in RFC7230>
The authz-server parameters contains the HTTPS URI, as defined in
[RFC7230], of the authorization server. The UA can discover metadata
about the AS using a mechanism like the one defined in [RFC8414].
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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 of this
document. The UAC will use the scope provided by the registrar to
contact the AS and obtain a proper token with the requested scope.
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".
5. Example Flows
5.1. Registration
The figure below shows 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.
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UA Registrar AS
---------------------------------------------------------------------
| | |
| [1] REGISTER | |
|------------------------------>| |
| | |
| [2] 401 Unauthorized | |
| WWW-Authenticate: Bearer "authz_server"="<authz_server>" |
|<------------------------------| |
| | |
| [3] The UA interacts with the AS and obtains tokens, using |
| some out of scope mechanism. |
|<=============================================================>|
| | |
| [4] REGISTER | |
| Authorization: Bearer <access_token> |
|------------------------------>| |
| | [5] HTTP POST /introspect |
| | {access_token} |
| |------------------------------>|
| | |
| | [6] 200 OK {metadata} |
| |<------------------------------|
| | |
| [7] 200 OK | |
|<------------------------------| |
| | |
In step [1], the UA starts the registration process by sending a SIP
REGISTER request to the registrar without any credentials.
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 interacts with the AS, potentially using the
OAuth Native App mechanism defined in [RFC8252], authenticates the
user and obtains the tokens needed to access the SIP service.
In step [4], the UA retries the registration process by sending a new
SIP REGISTER request that includes the access token that the UA
obtrained previously.
The registrar validates the access token. If the access token is a
reference token, the registrar MAY perform an introspection, as in
steps [5] and [6], in order to obtain more information about the
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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 [7], 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 below shows an example of a SIP registration, where the UA
has pre-configured information about the Authorization Server (AS)
from where to obtain the access token.
UA Registrar AS
---------------------------------------------------------------------
| | |
| [1] The UA interacts with the AS and obtains tokens, using |
| some out of scope mechanism. |
|<=============================================================>|
| | |
| [2] REGISTER | |
| Authorization: Bearer <access_token> |
|------------------------------>| |
| | [3] HTTP POST /introspect |
| | {access_token} |
| |------------------------------>|
| | |
| | [4] 200 OK {metadata} |
| |<------------------------------|
| | |
| [5] 200 OK | |
|<------------------------------| |
| | |
In step [1], the UA interacts with the AS, potentially using the
OAuth Native App mechanism defined in [RFC8252], authenticates the
user and obtains the tokens needed to access the SIP service.
In step [2], the UA retries the registration process by sending a new
SIP REGISTER request that includes the access token that the UA
obtrained previously.
The registrar validates the access token. If the access token is a
reference token, the registrar MAY perform an introspection, as in
steps [3] and [4], in order to obtain more information about the
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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 [5], 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 considerations also apply to SIP usage of
access token as defined in this document.
[RFC6749] mandates that 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.
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7. IANA Considerations
8. Acknowledgments
The authors would like to specially thank Paul Kyzivat for his
multiple detailed reviews and suggested text that significanly
improved the quality of the document.
The authors would also like to thank the following for their review
and feedback on this document:
Olle Johansson, Roman Shpount, Dale Worley, and Jorgen Axell.
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.
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>.
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[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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[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>.
[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>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
Authors' Addresses
Rifaat Shekh-Yusef
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
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Victor Pascual
webrtchacks
Spain
EMail: victor.pascual.avila@gmail.com
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