SIP Core R. Shekh-Yusef, Ed.
Internet-Draft Avaya
Updates: 3261 (if approved) C. Holmberg
Intended status: Standards Track Ericsson
Expires: August 9, 2018 V. Pascual
webrtchacks
February 5, 2018
Third-Party Authentication for Session Initiation Protocol (SIP)
draft-ietf-sipcore-sip-authn-02
Abstract
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.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. ID Token . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. SIP User Agent Types . . . . . . . . . . . . . . . . . . 5
1.5. Authentication Types . . . . . . . . . . . . . . . . . . 5
2. Authentication using the Authorization Code Flow . . . . . . 6
2.1. Public UA with Rich UI . . . . . . . . . . . . . . . . . 6
2.1.1. Initial Registration . . . . . . . . . . . . . . . . 7
2.1.2. Shared-Key . . . . . . . . . . . . . . . . . . . . . 8
2.1.3. Subsequent Registration . . . . . . . . . . . . . . . 8
2.1.4. Token Refresh . . . . . . . . . . . . . . . . . . . . 9
2.2. Public UA with Limited UI . . . . . . . . . . . . . . . . 10
2.2.1. Registration . . . . . . . . . . . . . . . . . . . . 10
2.2.2. Shared-Key . . . . . . . . . . . . . . . . . . . . . 11
2.2.3. Token Refresh . . . . . . . . . . . . . . . . . . . . 11
2.2.4. Subsequent Registration . . . . . . . . . . . . . . . 12
3. Authentication using the Resource Owner Password Credentials
flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Initial Registration . . . . . . . . . . . . . . . . . . 13
3.3. Subsequent Requests . . . . . . . . . . . . . . . . . . . 14
4. Authorization Header Syntax . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. Shared Key Feature-Capability Indicator . . . . . . . . . 15
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 16
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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 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.
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. 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.
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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.
Identity Provider (IdP)
This definition is borrowed from [MITKB]
"IdP (Identity Provider), is a system that creates, maintains,
and manages identity information for principals (users,
services, or systems) and provides principal authentication to
other service providers (applications) within a federation or
distributed network. It is a trusted third party that can be
relied upon by users and servers when users and servers are
establishing a dialog that must be authenticated. The IdP
sends an attribute assertion containing trusted information
about the user to the SP".
1.3. 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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1.4. 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.
1.5. 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 receiving 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 [RFC474bis].
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2. Authentication using the Authorization Code Flow
Authorization Code Flow is used by the SIP UA to authenticate to a
third-party IdP entity and 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.
2.1. Public UA with Rich UI
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 | |
| Location: AuthZ Server |
|<------------------------------| |
| | |
| | |
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 taken from the 200 OK |
| | |
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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.
2.1.1. Initial Registration
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.
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, using the "application/x-www-form-urlencoded"
format, 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 then contacts the Authorization Server and exchanges the
authorization code for access token, refresh token, and maybe ID
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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; otherwise, the proxy MUST reply
with 401 Unauthorized.
2.1.2. Shared-Key
The shared-key could be used to allow the UA to recover from a
connection loss to the server without the need to prompt the user for
credentials.
If the server supports the use of shared-key, it MUST indicate that
by adding the new sip.shared-key parameter to the feature-caps header
in the 200 OK response to the REGISTER request.
After sending the 200 OK to the UA to complete the registration
process, assuming that both the server and the client support his
feature, the proxy and the UA use the HMAC-SHA256(key, message) to
calculates the shared-key associated with this user as follows:
key
The authorization code obtained from the Authorization Server.
message
The concatenation of the 'from-tag', 'to-tag', and 'call-id' of
the 200 OK that completes the registration process.
2.1.3. Subsequent Registration
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, using the "application/x-www-
form-urlencoded" format:
grant_type (REQUIRED)
Value MUST be set to "proof_of_possession".
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pop (REQUIRED)
The pop calculated using the shared-key created the first time the
UA registered with the proxy.
The pop is calculated using the shared-key as follows:
pop = HMAC-SHA256(shared-key, digest-string)
See [RFC4474], section 9, for the SIP headers to hash to create
digest-string.
If the server supports the pop mechanism, then the server must
validate the pop provided by the client. If the validation is
successful, the server MUST reply with a 200 OK to complete the
registration process; otherwise, the server MUST reply with 401
Unauthorized.
2.1.4. Token Refresh
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.
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2.2. Public UA with Limited UI
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 an out-of-band mechanism (e.g.
a Browser or a One-Time-Password (OTP) application) 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 tokens |
| | from the authz server |
| |<----------------------------->|
| | |
| F2 200 OK | |
|<------------------------------| |
| | |
2.2.1. Registration
The UA will send a REGISTER request (F1) and include the code in the
body of the request, using the "application/x-www-form-urlencoded"
format, with the following parameters:
grant_type (REQUIRED)
Value MUST be set to "authorization_code".
code (REQUIRED)
The code received from the authorization server through the out-
of-bound mechanism.
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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; otherwise, the proxy MUST reply
with 401 Unauthorized.
2.2.2. Shared-Key
The shared-key could be used to allow the UA to recover from a
connection loss to the server without the need to prompt the user for
credentials.
If the server supports the use of shared-key, it MUST indicate that
by adding the new sip.shared-key parameter to the feature-caps header
in the 200 OK response to the REGISTER request.
After sending the 200 OK to the UA to complete the registration
process, assuming that both the server and the client support his
feature, the proxy and the UA use the HMAC-SHA256(key, message) to
calculates the shared-key associated with this user as follows:
key
The authorization code obtained from the Authorization Server.
message
The concatenation of the 'from-tag', 'to-tag', and 'call-id' of
the 200 OK that completes the registration process.
2.2.3. Token Refresh
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.
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2.2.4. Subsequent Registration
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 a proof-of-possession (pop) of the
shared-key in the body of the request, using the "application/x-www-
form-urlencoded" format:
grant_type (REQUIRED)
Value MUST be set to "proof_of_possession".
pop (REQUIRED)
The pop calculated using the shared-key created the first time the
UA registered with the proxy.
The pop is calculated using the shared-key as follows:
pop = HMAC-SHA256(shared-key, digest-string)
See [RFC4474], section 9, for the SIP headers to hash to create
digest-string.
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3. Authentication using the Resource Owner Password Credentials flow
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.
3.1. Overview
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 | |
|<------------------------------| |
| | |
3.2. Initial Registration
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.
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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.
3.3. 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. Authorization Header Syntax
This section describes the syntax of the authorization header with
the Bearer scheme.
Authorization = "Authorization" HCOLON "Bearer" LWS
"access_token" EQUAL access_token
access_token = quoted-string
5. Security Considerations
As this document uses the mechanism defined in the OAuth 2.0
[RFC6749], many of the security consideration in the OAuth 2.0
document apply to this document too.
The shared-key mechanism used with the Public UA allows a UA to re-
register without the need to obtain a new access code. If this
shared-key is leaked, an adversary will be able to register a UA and
impersonate the attacked user.
To reduce the chances of the shared-key being leaked, the UA should
not store the shared-key in a permanent storage, but keep it in
memory only.
A server should limit the use of shared-key to clients that are able
to provide an adequate level of protection for the shared-key. In
some deployments, the server might decide not to support the use of
shared-key at all.
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6. IANA Considerations
6.1. Shared Key Feature-Capability Indicator
This document defines the feature capability sip.shared-key in the
"SIP Feature-Capability Indicator Registration Tree" registry defined
in [RFC6809].
Name: sip.shared-key
Description: This feature-capability indicator, when included in a
Feature-Caps header field of a REGISTER response, indicates that the
server supports the use of shared-key mechanism.
Reference: [this document]
7. Acknowledgments
The authors would like to thank the following for their review and
feedback:
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.
Special thanks to Jon Peterson for a long discussion on the ideas and
concepts around the use of OpenID/OAuth as an authentication and
authorization mechanisms in a SIP network.
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8. References
8.1. Normative References
[MITKB] "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", 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.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", August 2006.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework",
RFC 6749, October 2012.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content", RFC 7231, June 2014.
[RFC7662] Richer, J., "OAuth 2.0 Token Introspection", RFC 7662,
October 2015.
8.2. Informative References
[RFC474bis]
Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in SIP",
https://datatracker.ietf.org/doc/draft-ietf-stir-
rfc4474bis/, February 2017.
Authors' Addresses
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Rifaat Shekh-Yusef (editor)
Avaya
250 Sidney Street
Belleville, Ontario
Canada
Phone: +1-613-967-5176
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
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