draft-ietf-sipcore-sip-token-authnz-17.txt   rfc8898.txt 
SIP Core R. Shekh-Yusef Internet Engineering Task Force (IETF) R. Shekh-Yusef
Internet-Draft Avaya Request for Comments: 8898 Auth0
Updates: 3261 (if approved) C. Holmberg Updates: 3261 C. Holmberg
Intended status: Standards Track Ericsson Category: Standards Track Ericsson
Expires: 6 November 2020 V. Pascual ISSN: 2070-1721 V. Pascual
webrtchacks Nokia
5 May 2020 September 2020
Third-Party Token-based Authentication and Authorization for Session Third-Party Token-Based Authentication and Authorization for Session
Initiation Protocol (SIP) Initiation Protocol (SIP)
draft-ietf-sipcore-sip-token-authnz-17
Abstract Abstract
This document defines the "Bearer" authentication scheme for the This document defines the "Bearer" authentication scheme for the
Session Initiation Protocol (SIP), and a mechanism by which user Session Initiation Protocol (SIP) and a mechanism by which user
authentication and SIP registration authorization is delegated to a authentication and SIP registration authorization is delegated to a
third party, using the OAuth 2.0 framework and OpenID Connect Core third party, using the OAuth 2.0 framework and OpenID Connect Core
1.0. This document updates RFC 3261 to provide guidance on how a SIP 1.0. This document updates RFC 3261 to provide guidance on how a SIP
User Agent Client (UAC) responds to a SIP 401/407 response that User Agent Client (UAC) responds to a SIP 401/407 response that
contains multiple WWW-Authenticate/Proxy-Authenticate header fields. contains multiple WWW-Authenticate/Proxy-Authenticate header fields.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 6 November 2020. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8898.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Applicability
1.3. Token Types and Formats . . . . . . . . . . . . . . . . . 3 1.3. Token Types and Formats
1.4. Example Flows . . . . . . . . . . . . . . . . . . . . . . 4 1.4. Example Flows
1.4.1. Registration . . . . . . . . . . . . . . . . . . . . 4 1.4.1. Registration
1.4.2. Registration with Preconfigured AS . . . . . . . . . 6 1.4.2. Registration with Preconfigured AS
2. SIP Procedures . . . . . . . . . . . . . . . . . . . . . . . 7 2. SIP Procedures
2.1. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 7 2.1. UAC Behavior
2.1.1. Obtaining Tokens and Responding to Challenges . . . . 7 2.1.1. Obtaining Tokens and Responding to Challenges
2.1.2. Protecting the Access Token . . . . . . . . . . . . . 9 2.1.2. Protecting the Access Token
2.1.3. REGISTER Request . . . . . . . . . . . . . . . . . . 9 2.1.3. REGISTER Request
2.1.4. Non-REGISTER Request . . . . . . . . . . . . . . . . 9 2.1.4. Non-REGISTER Request
2.2. User Agent Server (UAS) and Registrar Behavior . . . . . 10 2.2. User Agent Server (UAS) and Registrar Behavior
2.3. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 10 2.3. Proxy Behavior
3. Access Token Claims . . . . . . . . . . . . . . . . . . . . . 11 3. Access Token Claims
4. WWW-Authenticate Response Header Field . . . . . . . . . . . 11 4. WWW-Authenticate Response Header Field
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 5. Security Considerations
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations
6.1. New Proxy-Authenticate header field parameters . . . . . 14 6.1. New Proxy-Authenticate Header Field Parameters
6.2. New WWW-Authenticate header field parameters . . . . . . 14 6.2. New WWW-Authenticate Header Field Parameters
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 7. Normative References
8. Normative References . . . . . . . . . . . . . . . . . . . . 15 8. Informative References
9. Informative References . . . . . . . . . . . . . . . . . . . 16 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses
1. Introduction 1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] uses the same The Session Initiation Protocol (SIP) [RFC3261] uses the same
framework as HTTP [RFC7230] to authenticate users: a simple framework as HTTP [RFC7230] to authenticate users: a simple
challenge-response authentication mechanism that allows a SIP User challenge-response authentication mechanism that allows a SIP User
Agent Server (UAS), proxy or registrar to challenge a SIP User Agent Agent Server (UAS), proxy, or registrar to challenge a SIP User Agent
Client (UAC) request and allows the UAC to provide authentication Client (UAC) request and allows the UAC to provide authentication
information in response to that challenge. information in response to that challenge.
OAuth 2.0 [RFC6749] defines a token-based authorization framework to OAuth 2.0 [RFC6749] defines a token-based authorization framework to
allow an OAuth client to access resources on behalf of its user. allow an OAuth client to access resources on behalf of its user.
The OpenID Connect 1.0 specification [OPENID] defines a simple The OpenID Connect Core 1.0 specification [OPENID] defines a simple
identity layer on top of the OAuth 2.0 protocol, which enables OAuth/ identity layer on top of the OAuth 2.0 protocol, which enables OAuth/
OpenID clients to verify the identity of the user based on the OpenID clients to verify the identity of the user based on the
authentication performed by a dedicated authorization server (AS), authentication performed by a dedicated authorization server (AS),
referred to as OpenID Provider (OP), as well as to obtain basic referred to as OpenID Provider (OP), as well as to obtain basic
profile information about the user. profile information about the user.
This document defines the "Bearer" authentication scheme for the This document defines the "Bearer" authentication scheme for SIP and
Session Initiation Protocol (SIP), and a mechanism by which user a mechanism by which user authentication and SIP registration
authentication and SIP registration authorization is delegated to a authorization is delegated to a third party, using the OAuth 2.0
third party, using the OAuth 2.0 framework and OpenID Connect Core framework and OpenID Connect Core 1.0. This kind of user
1.0. This kind of user authentication enables single sign-on, which authentication enables single sign-on, which allows the user to
allows the user to authenticate once and gain access to both SIP and authenticate once and gain access to both SIP and non-SIP services.
non-SIP services.
This document also updates [RFC3261], by defining the UAC procedures This document also updates [RFC3261] by defining the UAC procedures
when a UAC receives a 401/407 response with multiple WWW- when a UAC receives a 401/407 response with multiple WWW-
Authenticate/Proxy-Authenticate header fields, providing challenges Authenticate/Proxy-Authenticate header fields, providing challenges
using different authentication schemes for the same realm. using different authentication schemes for the same realm.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Applicability 1.2. Applicability
This document covers cases where grants that allow the UAC to obtain This document covers cases where grants that allow the UAC to obtain
an access token from the AS are used. Cases where the UAC is not an access token from the AS are used. Cases where the UAC is not
able to obtain an access token (e.g., in the case of an authorization able to obtain an access token (e.g., in the case of an authorization
code grant) are not covered. code grant) are not covered.
1.3. Token Types and Formats 1.3. Token Types and Formats
The tokens used in third-party authorization depend on the type of The tokens used in third-party authorization depend on the type of
AS. AS.
An OAuth AS provides the following tokens to a successfully An OAuth AS provides the following tokens to a successfully
authorized UAC: authorized UAC:
* Access token: the UAC will use this token to gain access to Access Token:
services by providing the token to a SIP server. The UAC will use this token to gain access to services by
providing the token to a SIP server.
* Refresh token: the UAC will present this token to the AS to Refresh Token:
refresh a stale access token. The UAC will present this token to the AS to refresh a stale
access token.
An OP returns an additional token: An OP returns an additional token:
* ID Token: this token contains a SIP URI associated with the user ID Token:
and other user-specific details that will be consumed by the UAC. This token contains a SIP URI associated with the user and other
user-specific details that will be consumed by the UAC.
Tokens can be represented in two different formats: Tokens can be represented in two different formats:
* Structured Token: a token that consists of a structured object Structured Token:
that contains the claims associated with the token, e.g., JSON Web A token that consists of a structured object that contains the
Token (JWT) as defined in [RFC7519]. claims associated with the token, e.g., JSON Web Token (JWT), as
defined in [RFC7519].
* Reference Token: a token that consists of an opaque string that is Reference Token:
used to obtain the details of the token and its associated claims, A token that consists of an opaque string that is used to obtain
as defined in [RFC6749]. the details of the token and its associated claims, as defined in
[RFC6749].
Access Tokens are represented in one of the above two formats. Access tokens are represented in one of the above two formats.
Refresh Tokens usually are represented in a reference format, as this Refresh tokens usually are represented in a reference format, as this
token is consumed only the AS that issued the token. ID Token is token is consumed only by the AS that issued the token. The ID token
defined as a structured token in the form of a JWT. is defined as a structured token in the form of a JWT.
1.4. Example Flows 1.4. Example Flows
1.4.1. Registration 1.4.1. Registration
Figure 1 below shows an example of a SIP registration, where the Figure 1 below shows an example of a SIP registration where the
registrar informs the UAC about the AS from which the UAC can obtain registrar informs the UAC about the AS from which the UAC can obtain
an access token. an access token.
UAC Registrar AS/OP UAC Registrar AS/OP
--------------------------------------------------------------------- ---------------------------------------------------------------------
| | | | | |
| [1] REGISTER | | | [1] REGISTER | |
|------------------------------>| | |------------------------------>| |
| | | | | |
| [2] 401 Unauthorized | | | [2] 401 Unauthorized | |
| WWW-Authenticate: Bearer "authz_server"="<authz_server>" | | WWW-Authenticate: Bearer "authz_server"="<authz_server>" |
|<------------------------------| | |<------------------------------| |
| | | | | |
| [3] The UAC interacts with the AS and obtains tokens, using | | [3] The UAC interacts with the AS and obtains tokens using |
| some out-of-scope mechanism. | | some out-of-scope mechanism. |
|<=============================================================>| |<=============================================================>|
| | | | | |
| [4] REGISTER | | | [4] REGISTER | |
| Authorization: Bearer <access_token> | | Authorization: Bearer <access_token> |
|------------------------------>| | |------------------------------>| |
| | [5] HTTP POST /introspect | | | [5] HTTP POST /introspect |
| | {access_token} | | | {access_token} |
| | (OPTIONAL) | | | (OPTIONAL) |
| |------------------------------>| | |------------------------------>|
skipping to change at page 5, line 40 skipping to change at line 208
| | | | | |
| [7] 200 OK | | | [7] 200 OK | |
|<------------------------------| | |<------------------------------| |
| | | | | |
Figure 1: Example Registration Flow Figure 1: Example Registration Flow
In step [1], the UAC starts the registration process by sending a SIP In step [1], the UAC starts the registration process by sending a SIP
REGISTER request to the registrar without any credentials. REGISTER request to the registrar without any credentials.
In step [2], the registrar challenges the UA, by sending a SIP 401 In step [2], the registrar challenges the UA by sending a SIP 401
(Unauthorized) response to the REGISTER request. In the response, (Unauthorized) response to the REGISTER request. In the response,
the registrar includes information about the AS to contact in order the registrar includes information about the AS to contact in order
to obtain a token. to obtain a token.
In step [3], the UAC interacts with the AS via an out-of-scope In step [3], the UAC interacts with the AS via an out-of-scope
mechanism, potentially using the OAuth Native App mechanism defined mechanism, potentially using the OAuth Native App mechanism defined
in [RFC8252]. The AS authenticates the user and provides the UAC in [RFC8252]. The AS authenticates the user and provides the UAC
with the tokens needed to access the SIP service. with the tokens needed to access the SIP service.
In step [4], the UAC retries the registration process by sending a In step [4], the UAC retries the registration process by sending a
skipping to change at page 6, line 25 skipping to change at line 242
1.4.2. Registration with Preconfigured AS 1.4.2. Registration with Preconfigured AS
Figure 2 shows an example of a SIP registration where the UAC has Figure 2 shows an example of a SIP registration where the UAC has
been preconfigured with information about the AS from which to obtain been preconfigured with information about the AS from which to obtain
the access token. the access token.
UAC Registrar AS/OP UAC Registrar AS/OP
--------------------------------------------------------------------- ---------------------------------------------------------------------
| | | | | |
| [1] The UAC interacts with the AS and obtains tokens, using | | [1] The UAC interacts with the AS and obtains tokens using |
| some out of scope mechanism. | | some out-of-scope mechanism. |
|<=============================================================>| |<=============================================================>|
| | | | | |
| [2] REGISTER | | | [2] REGISTER | |
| Authorization: Bearer <access_token> | | Authorization: Bearer <access_token> |
|------------------------------>| | |------------------------------>| |
| | [3] HTTP POST /introspect | | | [3] HTTP POST /introspect |
| | {access_token} | | | {access_token} |
| | (OPTIONAL) | | | (OPTIONAL) |
| |------------------------------>| | |------------------------------>|
| | | | | |
skipping to change at page 7, line 23 skipping to change at line 287
Otherwise, after the registrar validates the token, it inspects its Otherwise, after the registrar validates the token, it inspects its
claims and acts upon it. claims and acts upon it.
In step [5], once the registrar has successfully verified and In step [5], once the registrar has successfully verified and
accepted the access token, it sends a 200 (OK) response to the accepted the access token, it sends a 200 (OK) response to the
REGISTER request. REGISTER request.
2. SIP Procedures 2. SIP Procedures
Section 22 of [RFC3261] defines the SIP procedures for the Digest Section 22 of [RFC3261] defines the SIP procedures for the Digest
authentication mechanism. The same procedures apply to the Bearer authentication mechanism. The same procedures apply to the "Bearer"
authentication mechanism, with the changes described in this section. authentication mechanism, with the changes described in this section.
2.1. UAC Behavior 2.1. UAC Behavior
2.1.1. Obtaining Tokens and Responding to Challenges 2.1.1. Obtaining Tokens and Responding to Challenges
When a UAC sends a request without credentials (or with invalid When a UAC sends a request without credentials (or with invalid
credentials), it could receive either a 401 (Unauthorized) response credentials), it could receive either a 401 (Unauthorized) response
with a WWW-Authenticate header field or a 407 (Proxy Authentication with a WWW-Authenticate header field or a 407 (Proxy Authentication
Required) response with a Proxy-Authenticate header field. If the Required) response with a Proxy-Authenticate header field. If the
WWW-Authenticate or Proxy-Authenticate header field indicates WWW-Authenticate or Proxy-Authenticate header field indicates
"Bearer" scheme authentication and contains an address to an AS, the "Bearer" scheme authentication and contains an address to an AS, the
UAC contacts the AS in order to obtain tokens, and includes the UAC contacts the AS in order to obtain tokens and includes the
requested scopes, based on a local configuration (Figure 1). The UAC requested scopes, based on a local configuration (Figure 1). The UAC
MUST check the AS URL received in the 401/407 response against a list MUST check the AS URL received in the 401/407 response against a list
of trusted ASs configured on the UAC, in order to prevent several of trusted ASs configured on the UAC in order to prevent several
classes of possible vulnerabilities when a client blindly attempts to classes of possible vulnerabilities when a client blindly attempts to
use any provided AS. use any provided AS.
The detailed OAuth2 procedure to authenticate the user and obtain The detailed OAuth2 procedure to authenticate the user and obtain
these tokens is out of scope of this document. The address of the AS these tokens is out of scope of this document. The address of the AS
might already be known to the UAC via configuration. In such cases, might already be known to the UAC via configuration. In such cases,
the UAC can contact the AS for tokens before it sends a SIP request the UAC can contact the AS for tokens before it sends a SIP request
(Figure 2). Procedures for native applications are defined in (Figure 2). Procedures for native applications are defined in
[RFC8252]. When using the mechanism defined in [RFC8252] the user of [RFC8252]. When using the mechanism defined in [RFC8252], the user
the UAC will be directed to interact with the AS using a web browser, of the UAC will be directed to interact with the AS using a web
allowing the AS to prompt the user for multi-factor authentication, browser, which allows the AS to prompt the user for multi-factor
to redirect the user to third-party identity providers, and to enable authentication, to redirect the user to third-party identity
the use of single sign-on sessions. providers, and to enable the use of single sign-on sessions.
The tokens returned to the UAC depend on the type of AS: an OAuth AS The tokens returned to the UAC depend on the type of AS; an OAuth AS
provides an access token and optionally a refresh token [RFC6749]. provides an access token and, optionally, a refresh token [RFC6749].
The refresh token is only used between the UAC and the AS. If the AS The refresh token is only used between the UAC and the AS. If the AS
provides a refresh token to the UAC, the UAC uses it to request a new provides a refresh token to the UAC, the UAC uses it to request a new
access token from the AS before the currently used access token access token from the AS before the currently used access token
expires ([RFC6749], Section 1.5). If the AS does not provide a expires ([RFC6749], Section 1.5). If the AS does not provide a
refresh token, the UAC needs to re-authenticate the user, in order to refresh token, the UAC needs to reauthenticate the user in order to
get a new access token, before the currently used access token get a new access token before the currently used access token
expires. An OP returns an additional ID Token that contains claims expires. An OP returns an additional ID token that contains claims
about the authentication of the user by an authorization server. The about the authentication of the user by an authorization server. The
ID Token can potentially include other optional claims about the ID token can potentially include other optional claims about the
user, e.g. the SIP URI, that will be consumed by the UAC and later user, e.g., the SIP URI, that will be consumed by the UAC and later
used to register with the registrar. used to register with the registrar.
If the UAC receives a 401/407 response with multiple WWW- If the UAC receives a 401/407 response with multiple WWW-
Authenticate/Proxy-Authenticate header fields, providing challenges Authenticate/Proxy-Authenticate header fields, providing challenges
using different authentication schemes for the same realm, the UAC using different authentication schemes for the same realm, the UAC
provides credentials for one of the schemes that it supports, based provides credentials for one of the schemes that it supports, based
on local policy. on local policy.
NOTE: At the time of writing this document, detailed procedures for | NOTE: At the time of writing, detailed procedures for the cases
the cases where a UAC receives multiple different authentication | where a UAC receives multiple different authentication schemes
schemes had not been defined. A future specification might define | had not been defined. A future specification might define such
such procedures. | procedures.
NOTE: The address of the AS might be known to the UAC e.g., using | NOTE: The address of the AS might be known to the UAC, e.g.,
means of configuration, in which case the UAC can contact the AS in | using means of configuration, in which case the UAC can contact
order to obtain the access token before it sends SIP request without | the AS in order to obtain the access token before it sends SIP
credentials. | request without credentials.
2.1.2. Protecting the Access Token 2.1.2. Protecting the Access Token
[RFC6749] mandates that access tokens are protected with TLS when in [RFC6749] mandates that access tokens are protected with TLS when in
transit. However, SIP makes use of intermediary SIP proxies, and TLS transit. However, SIP makes use of intermediary SIP proxies, and TLS
only guarantees hop-to-hop protection when used to protect SIP only guarantees hop-to-hop protection when used to protect SIP
signaling. Therefore the access token MUST be protected in a way so signaling. Therefore, the access token MUST be protected in a way so
that only authorized SIP servers will have access to it. SIP that only authorized SIP servers will have access to it. SIP
endpoints that support this document MUST use encrypted JSON Web endpoints that support this document MUST use encrypted JWTs
Tokens (JWT) [RFC7519] for encoding and protecting access tokens when [RFC7519] for encoding and protecting access tokens when they are
they are included in SIP requests, unless some other mechanism is included in SIP requests, unless some other mechanism is used to
used to guarantee that only authorized SIP endpoints have access to guarantee that only authorized SIP endpoints have access to the
the access token. TLS can still be used for protecting traffic access token. TLS can still be used for protecting traffic between
between SIP endpoints and the AS, as defined in [RFC6749]. SIP endpoints and the AS, as defined in [RFC6749].
2.1.3. REGISTER Request 2.1.3. REGISTER Request
The procedures in this section apply when the UAC has received a The procedures in this section apply when the UAC has received a
challenge that contains a "Bearer" scheme, and the UAC has obtained a challenge that contains a "Bearer" scheme and the UAC has obtained a
token as specified in Section 2.1.1. token, as specified in Section 2.1.1.
The UAC sends a REGISTER request with an Authorization header field The UAC sends a REGISTER request with an Authorization header field
containing the response to the challenge, including the Bearer scheme containing the response to the challenge, including the "Bearer"
carrying a valid access token in the request, as specified in scheme carrying a valid access token in the request, as specified in
[RFC6750]. [RFC6750].
Note that, if there were multiple challenges with different schemes, Note that if there were multiple challenges with different schemes,
then the UAC may be able to successfully retry the request using non- then the UAC may be able to successfully retry the request using
Bearer credentials. non-"Bearer" credentials.
Typically, a UAC will obtain a new access token for each new binding, Typically, a UAC will obtain a new access token for each new binding.
However, based on local policy, a UAC MAY include an access token However, based on local policy, a UAC MAY include an access token
that has been used for another binding associated with the same that has been used for another binding associated with the same
Address Of Record (AOR) in the request. Address Of Record (AOR) in the request.
If the access token included in a REGISTER request is not accepted, 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 and the UAC receives a 401 response or a 407 response, the UAC
follows the procedures in Section 2.1.1. follows the procedures in Section 2.1.1.
2.1.4. Non-REGISTER Request 2.1.4. Non-REGISTER Request
The procedures in this section apply when the UAC has received a The procedures in this section apply when the UAC has received a
challenge that contains a "Bearer" scheme, and the UAC has obtained a challenge that contains a "Bearer" scheme and the UAC has obtained a
token as specified in Section 2.1.1. token, as specified in Section 2.1.1.
When the UAC sends a request, it MUST include an Authorization header When the UAC sends a request, it MUST include an Authorization header
field with a Bearer scheme, carrying a valid access token obtained field with a "Bearer" scheme carrying a valid access token obtained
from the AS indicated in the challenge, in the request, as specified from the AS indicated in the challenge in the request, as specified
in [RFC6750]. Based on local policy, the UAC MAY include an access in [RFC6750]. Based on local policy, the UAC MAY include an access
token that has been used for another dialog, or for another stand- token that has been used for another dialog, or for another stand-
alone request, if the target of the new request is the same. 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 If the access token included in a request is not accepted and the UAC
UAC receives a 401 response or a 407 response, the UAC follows the receives a 401 response or a 407 response, the UAC follows the
procedures in Section 2.1.1. procedures in Section 2.1.1.
2.2. User Agent Server (UAS) and Registrar Behavior 2.2. User Agent Server (UAS) and Registrar Behavior
When a UAS or registrar receives a request that fails to contain When a UAS or registrar receives a request that fails to contain
authorization credentials acceptable to it, the UAS/registrar SHOULD authorization credentials acceptable to it, the UAS/registrar SHOULD
challenge the request by sending a 401 (Unauthorized) response. If challenge the request by sending a 401 (Unauthorized) response. If
the UAS/registrar chooses to challenge the request, and is willing to the UAS/registrar chooses to challenge the request and is willing to
accept an access token as a credential, it MUST include a WWW- accept an access token as a credential, it MUST include a WWW-
Authenticate header field in the response that indicates "Bearer" Authenticate header field in the response that indicates a "Bearer"
scheme and includes an AS address, encoded as an https URI [RFC7230], scheme and includes an AS address, encoded as an https URI [RFC7230],
from which the UAC can obtain an access token. from which the UAC can obtain an access token.
When a UAS or registrar receives a SIP request that contains an When a UAS or registrar receives a SIP request that contains an
Authorization header field with an access token, the UAS/registrar Authorization header field with an access token, the UAS/registrar
MUST validate the access token, using the procedures associated with MUST validate the access token using the procedures associated with
the type of access token (Structured or Reference) used, e.g., the type of access token (structured or reference) used, e.g.,
[RFC7519]. If the token provided is an expired access token, then [RFC7519]. If the token provided is an expired access token, then
the UAS/registrar MUST reply with a 401 (Unauthorized) response, as the UAS/registrar MUST reply with a 401 (Unauthorized) response, as
defined in section 3 of [RFC6750]. If the validation is successful, defined in Section 3 of [RFC6750]. If the validation is successful,
the UAS/registrar can continue to process the request using normal the UAS/registrar can continue to process the request using normal
SIP procedures. If the validation fails, the UAS/registrar MUST SIP procedures. If the validation fails, the UAS/registrar MUST
reply with 401 (Unauthorized) response. reply with a 401 (Unauthorized) response.
2.3. Proxy Behavior 2.3. Proxy Behavior
When a proxy receives a request that fails to contain authorization When a proxy receives a request that fails to contain authorization
credentials acceptable to it, it SHOULD challenge the request by credentials acceptable to it, it SHOULD challenge the request by
sending a 407 (Proxy Authentication Required) response. If the proxy sending a 407 (Proxy Authentication Required) response. If the proxy
chooses to challenge the request, and is willing to accept an access chooses to challenge the request and is willing to accept an access
token as a credential, it MUST include a Proxy-Authenticate header token as a credential, it MUST include a Proxy-Authenticate header
field in the response that indicates "Bearer" scheme and includes an field in the response that indicates a "Bearer" scheme and includes
AS address, encoded as an https URI [RFC7230], from which the UAC can an AS address, encoded as an https URI [RFC7230], from which the UAC
obtain an access token. can obtain an access token.
When a proxy wishes to authenticate a received request, it MUST When a proxy wishes to authenticate a received request, it MUST
search the request for Proxy-Authorization header fields with 'realm' search the request for Proxy-Authorization header fields with 'realm'
parameters that match its realm. It then MUST successfully validate parameters that match its realm. It then MUST successfully validate
the credentials from at least one Proxy-Authorization header field the credentials from at least one Proxy-Authorization header field
for its realm. When the scheme is "Bearer", the proxy MUST validate for its realm. When the scheme is "Bearer", the proxy MUST validate
the access token, using the procedures associated with the type of the access token using the procedures associated with the type of
access token (Structured or Reference) used, e.g., [RFC7519]. access token (structured or reference) used, e.g., [RFC7519].
3. Access Token Claims 3. Access Token Claims
The type of services to which an access token grants access can be The type of services to which an access token grants access can be
determined using different methods. The methods used and the access determined using different methods. The methods used and the access
provided by the token are based on local policy agreed between the AS provided by the token are based on local policy agreed between the AS
and the registrar. and the registrar.
If an access token is encoded as a JWT, it will contain a list of If an access token is encoded as a JWT, it will contain a list of
claims [RFC7519], including both registered and application-specific claims [RFC7519], including both registered and application-specific
skipping to change at page 11, line 33 skipping to change at line 464
claims, some other mechanism, or a combination of claims and some claims, some other mechanism, or a combination of claims and some
other mechanism. If an access token is a reference token, the other mechanism. If an access token is a reference token, the
registrar will grant access based on some other mechanism. Examples registrar will grant access based on some other mechanism. Examples
of such other mechanisms are introspection [RFC7662] and user profile of such other mechanisms are introspection [RFC7662] and user profile
lookups. lookups.
4. WWW-Authenticate Response Header Field 4. WWW-Authenticate Response Header Field
This section uses ABNF [RFC5234] to describe the syntax of the WWW- This section uses ABNF [RFC5234] to describe the syntax of the WWW-
Authenticate header field when used with the "Bearer" scheme to Authenticate header field when used with the "Bearer" scheme to
challenge the UAC for credentials, by extending the 'challenge' challenge the UAC for credentials by extending the 'challenge'
parameter defined by [RFC3261]. parameter defined by [RFC3261].
challenge =/ ("Bearer" LWS bearer-cln *(COMMA bearer-cln)) challenge =/ ("Bearer" LWS bearer-cln *(COMMA bearer-cln))
bearer-cln = realm / scope-param / authz-server-param / error-param / bearer-cln = realm / scope-param / authz-server-param / error-param /
auth-param auth-param
realm = <defined in RFC3261> realm = <defined in RFC 3261>
scope-param = "scope" EQUAL DQUOTE scope DQUTE scope-param = "scope" EQUAL DQUOTE scope DQUOTE
scope = <defined in RFC6749> scope = <defined in RFC 6749>
authz-server-param = "authz_server" EQUAL DQUOTE authz-server DQUOTE authz-server-param = "authz_server" EQUAL DQUOTE authz-server DQUOTE
authz-server = https-URI authz-server = https-URI
https-URI = <defined in RFC7230> https-URI = <defined in RFC 7230>
error-param = "error" EQUAL DQUOTE error DQUOTE error-param = "error" EQUAL DQUOTE error DQUOTE
error = <defined in RFC6749> error = <defined in RFC 6749>
auth-param = <defined in RFC3261> auth-param = <defined in RFC 3261>
Figure 3: Bearer Scheme Syntax Figure 3: "Bearer" Scheme Syntax
The authz_server parameter contains the HTTPS URI, as defined in The authz_server parameter contains the HTTPS URI, as defined in
[RFC7230], of the AS. The UAC can discover metadata about the AS [RFC7230], of the AS. The UAC can discover metadata about the AS
using a mechanism like the one defined in [RFC8414]. using a mechanism like the one defined in [RFC8414].
The realm and auth-param parameters are defined in [RFC3261]. The realm and auth-param parameters are defined in [RFC3261].
Per [RFC3261], the realm string alone defines the protection domain. Per [RFC3261], "the realm string alone defines the protection
[RFC3261] states that the realm string must be globally unique and domain". [RFC3261] states that the realm string must be globally
recommends that the realm string contain a hostname or domain name. unique and recommends that the realm string contain a hostname or
It also states that the realm string should be a human-readable domain name. It also states that the realm string should be a human-
identifier that can be rendered to the user. readable identifier that can be rendered to the user.
The scope and error parameters are defined in [RFC6749]. The scope and error parameters are defined in [RFC6749].
The scope parameter can be used by the registrar/proxy to indicate to The scope parameter can be used by the registrar/proxy to indicate to
the UAC the minimum scope that must be associated with the access 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 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, of the scope parameter is expressed as a list of space-delimited,
case-sensitive strings. The strings are defined by the AS. The case-sensitive strings. The strings are defined by the AS. The
values of the scope parameter are out of scope of this document. The values of the scope parameter are out of scope of this document. The
UAC will use the scope provided by the registrar to contact the AS UAC will use the scope provided by the registrar to contact the AS
and obtain a proper token with the requested scope. and obtain a proper token with the requested scope.
The error parameter could be used by the registrar/proxy to indicate The error parameter could be used by the registrar/proxy to indicate
to the UAC the reason for the error, with possible values of to the UAC the reason for the error, with possible values of
"invalid_token" or "invalid_scope". "invalid_token" or "invalid_scope".
5. Security Considerations 5. Security Considerations
The security considerations for OAuth are defined in [RFC6749]. The The security considerations for OAuth are defined in [RFC6749]. The
security considerations for bearer tokens are defined in [RFC6750]. security considerations for "Bearer" tokens are defined in [RFC6750].
The security considerations for JSON Web Tokens (JWT) are defined in The security considerations for JWTs are defined in [RFC7519]. These
[RFC7519]. These security considerations also apply to SIP usage of security considerations also apply to SIP usage of access tokens, as
access token as defined in this document. defined in this document.
[RFC6749] mandates that access tokens are protected with TLS when in [RFC6749] mandates that access tokens are protected with TLS when in
transit. However, SIP makes have use of intermediary SIP proxies, transit. However, SIP makes use of intermediary SIP proxies, and TLS
and TLS only guarantees hop-to-hop protection when used to protect only guarantees hop-to-hop protection when used to protect SIP
SIP signaling. Therefore the access token MUST be protected in a way signaling. Therefore, the access token MUST be protected in a way so
so that only authorized SIP servers will have access to it. SIP that only authorized SIP servers will have access to it. SIP
endpoints that support this document MUST use encrypted JSON Web endpoints that support this document MUST use encrypted JWTs
Tokens (JWT) [RFC7519] for encoding and protecting access tokens when [RFC7519] for encoding and protecting access tokens when they are
they are included in SIP requests, unless some other mechanism is included in SIP requests, unless some other mechanism is used to
used to guarantee that only authorized SIP endpoints have access to guarantee that only authorized SIP endpoints have access to the
the access token. TLS can still be used for protecting traffic access token. TLS can still be used for protecting traffic between
between SIP endpoints and the AS, as defined in [RFC6749]. SIP endpoints and the AS, as defined in [RFC6749].
Single Sign-On (SSO) enables the user to use one set of credentials Single Sign-On (SSO) enables the user to use one set of credentials
to authenticate once and gain access to multiple SIP and non-SIP to authenticate once and gain access to multiple SIP and non-SIP
services using access token(s). If the SSO login is compromised, services using access token(s). If the SSO login is compromised,
that single point of compromise has a much broader effect than is the that single point of compromise has a much broader effect than is the
case without SSO. Further, an attacker can often use a compromised case without SSO. Further, an attacker can often use a compromised
account to set up Single Sign-On for other services that the victim account to set up Single Sign-On for other services that the victim
has not established an account with, and sometimes can even switch a has not established an account with and sometimes can even switch a
dedicated account into Single-Sign-On mode, creating a still broader dedicated account into SSO mode, creating a still broader attack.
attack.
Because of that, it is critical to make sure that extra security Because of that, it is critical to make sure that extra security
measures be taken to safeguard credentials used for Single Sign-On. measures be taken to safeguard credentials used for Single Sign-On.
Examples of such measures include long passphrase instead of a Examples of such measures include a long passphrase instead of a
password, enabling multi-factor factor authentication, and the use of password, enabling multi-factor authentication, and the use of the
the native platform browser when possible, as defined in [RFC8252]. native platform browser when possible, as defined in [RFC8252].
Although this is out of scope for this document, it is important to Although this is out of scope for this document, it is important to
carefully consider the claims provided in the tokens used to access carefully consider the claims provided in the tokens used to access
these services to make sure of the privacy of the user accessing these services to make sure of the privacy of the user accessing
these services. As mentioned above, this document calls for these services. As mentioned above, this document calls for
encrypting JWT representing the access token. encrypting JWTs representing the access token.
It is important that both parties participating in SSO provide It is important that both parties participating in SSO provide
mechanisms for users to sever the SSO relationship, so that it is mechanisms for users to sever the SSO relationship so that it is
possible without undue difficulty to mitigate a compromise that has possible without undue difficulty to mitigate a compromise that has
already happened. already happened.
The operator of a Single-Sign-On authentication system has access to The operator of an SSO authentication system has access to private
private information about sites and services that their users log information about sites and services that their users log into and
into, and even, to some extent, about their usage patterns. It's even, to some extent, their usage patterns. It's important to call
important to call these out in privacy disclosures and policies, and these out in privacy disclosures and policies and to make sure that
to make sure that users can be aware of the tradeoffs between users can be aware of the trade-offs between convenience and privacy
convenience and privacy when they choose to use SSO. when they choose to use SSO.
When a registrar chooses to challenge a REGISTER request, if the When a registrar chooses to challenge a REGISTER request, if the
registrar can provide access to different levels of services, it is registrar can provide access to different levels of services, it is
RECOMMENDED that the registrar includes a scope in the response in RECOMMENDED that the registrar include a scope in the response in
order to indicate the minimum scope needed to register and access order to indicate the minimum scope needed to register and access
basic services. The access token might include an extended scope basic services. The access token might include an extended scope
that gives the user access to more advanced features beyond basic that gives the user access to more advanced features beyond basic
services. In SIP, the AS administrator will typically decide what services. In SIP, the AS administrator will typically decide what
level of access is provided for a given user. level of access is provided for a given user.
The UAC MUST check the AS URL received in the 401/407 response The UAC MUST check the AS URL received in the 401/407 response
against a list of trusted ASs configured on the UAC, in order to against a list of trusted ASs configured on the UAC in order to
prevent several classes of possible vulnerabilities when a client prevent several classes of possible vulnerabilities when a client
blindly attempts to use any provided AS. blindly attempts to use any provided AS.
6. IANA Considerations 6. IANA Considerations
6.1. New Proxy-Authenticate header field parameters 6.1. New Proxy-Authenticate Header Field Parameters
This section defines new SIP header field parameters in the "Header This section defines new SIP header field parameters in the "Header
Field Parameters and Parameter Values" subregistry of the "Session Field Parameters and Parameter Values" subregistry of the "Session
Initiation Protocol (SIP) Parameters" registry: Initiation Protocol (SIP) Parameters" registry:
https://www.iana.org/assignments/sip-parameters <https://www.iana.org/assignments/sip-parameters>
Header Field: Proxy-Authenticate
Parameter Name: authz_server
Predefined Values: No
Reference: RFC XXXX
Parameter Name: error
Predefined Values: No
Reference: RFC XXXX
Parameter Name: scope +================+===================+===========+
Predefined Values: No | Parameter Name | Predefined Values | Reference |
Reference: RFC XXXX +================+===================+===========+
| authz_server | No | RFC 8898 |
+----------------+-------------------+-----------+
| error | No | RFC 8898 |
+----------------+-------------------+-----------+
| scope | No | RFC 8898 |
+----------------+-------------------+-----------+
Figure 4 Table 1: Header Field: Proxy-Authenticate
6.2. New WWW-Authenticate header field parameters 6.2. New WWW-Authenticate Header Field Parameters
This section defines new SIP header field parameters in the "Header This section defines new SIP header field parameters in the "Header
Field Parameters and Parameter Values" subregistry of the "Session Field Parameters and Parameter Values" subregistry of the "Session
Initiation Protocol (SIP) Parameters" registry: Initiation Protocol (SIP) Parameters" registry:
https://www.iana.org/assignments/sip-parameters <https://www.iana.org/assignments/sip-parameters>
Header Field: WWW-Authenticate
Parameter Name: authz_server
Predefined Values: No
Reference: RFC XXXX
Parameter Name: error
Predefined Values: No
Reference: RFC XXXX
Parameter Name: scope
Predefined Values: No
Reference: RFC XXXX
Figure 5
7. Acknowledgments
The authors would like to specially thank Paul Kyzivat for his
multiple detailed reviews and suggested text that significantly
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, Dale Worley, and Yehoshua Gev.
Roman Danyliw, Benjamin Kaduk, Erik Kline, Barry Leiba, Eric Vyncke +================+===================+===========+
and Magnus Westerlund provided feedback and suggestions for | Parameter Name | Predefined Values | Reference |
improvements as part of the IESG evaluation of the document. Special +================+===================+===========+
thanks to Benjamin Kaduk for his detailed and comprehensive reviews | authz_server | No | RFC 8898 |
and comments. +----------------+-------------------+-----------+
| error | No | RFC 8898 |
+----------------+-------------------+-----------+
| scope | No | RFC 8898 |
+----------------+-------------------+-----------+
The authors would also like to specially thank Jean Mahoney for her Table 2: Header Field: WWW-Authenticate
multiple reviews, editorial help, and the coversion of the XML source
file from v2 to v3.
8. Normative References 7. Normative References
[OPENID] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and [OPENID] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", February 2014. C. Mortimore, "OpenID Connect Core 1.0", February 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
skipping to change at page 16, line 42 skipping to change at line 663
<https://www.rfc-editor.org/info/rfc7519>. <https://www.rfc-editor.org/info/rfc7519>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015, RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>. <https://www.rfc-editor.org/info/rfc7662>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9. Informative References 8. Informative References
[RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps", [RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017, BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>. <https://www.rfc-editor.org/info/rfc8252>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 [RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414, Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018, DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>. <https://www.rfc-editor.org/info/rfc8414>.
Acknowledgments
The authors would like to specially thank Paul Kyzivat for his
multiple detailed reviews and suggested text that significantly
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, Dale Worley, and Yehoshua Gev.
Roman Danyliw, Benjamin Kaduk, Erik Kline, Barry Leiba, Eric Vyncke,
and Magnus Westerlund provided feedback and suggestions for
improvements as part of the IESG evaluation of the document. Special
thanks to Benjamin Kaduk for his detailed and comprehensive reviews
and comments.
The authors would also like to specially thank Jean Mahoney for her
multiple reviews, editorial help, and the conversion of the XML
source file from v2 to v3.
Authors' Addresses Authors' Addresses
Rifaat Shekh-Yusef Rifaat Shekh-Yusef
Avaya Auth0
425 Legget Drive
Ottawa Ontario Ottawa Ontario
Canada Canada
Phone: +1-613-595-9106 Email: rifaat.s.ietf@gmail.com
Email: rifaat.ietf@gmail.com
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
FI- Jorvas 02420 FI-02420 Jorvas
Finland Finland
Email: christer.holmberg@ericsson.com Email: christer.holmberg@ericsson.com
Victor Pascual Victor Pascual
webrtchacks Nokia
Barcelona
Spain Spain
Email: victor.pascual.avila@gmail.com Email: victor.pascual_avila@nokia.com
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