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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIP Core R. Shekh-Yusef 3 Internet-Draft Avaya 4 Updates: 3261 (if approved) C. Holmberg 5 Intended status: Standards Track Ericsson 6 Expires: 21 August 2020 V. Pascual 7 webrtchacks 8 18 February 2020 10 Third-Party Token-based Authentication and Authorization for Session 11 Initiation Protocol (SIP) 12 draft-ietf-sipcore-sip-token-authnz-08 14 Abstract 16 This document defines a SIP mechanism that relies on the OAuth 2.0 17 and OpenID Connect Core 1.0 to enable delegation of the user 18 authentication and SIP registration authorization to a third-party. 19 The document updates RFC 3261. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on 21 August 2020. 38 Copyright Notice 40 Copyright (c) 2020 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 45 license-info) in effect on the date of publication of this document. 46 Please review these documents carefully, as they describe your rights 47 and restrictions with respect to this document. Code Components 48 extracted from this document must include Simplified BSD License text 49 as described in Section 4.e of the Trust Legal Provisions and are 50 provided without warranty as described in the Simplified BSD License. 52 This document may contain material from IETF Documents or IETF 53 Contributions published or made publicly available before November 54 10, 2008. The person(s) controlling the copyright in some of this 55 material may not have granted the IETF Trust the right to allow 56 modifications of such material outside the IETF Standards Process. 57 Without obtaining an adequate license from the person(s) controlling 58 the copyright in such materials, this document may not be modified 59 outside the IETF Standards Process, and derivative works of it may 60 not be created outside the IETF Standards Process, except to format 61 it for publication as an RFC or to translate it into languages other 62 than English. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 68 1.2. SIP User Agent Types . . . . . . . . . . . . . . . . . . 3 69 2. SIP Procedures . . . . . . . . . . . . . . . . . . . . . . . 4 70 2.1. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 4 71 2.1.1. Obtaining Tokens . . . . . . . . . . . . . . . . . . 4 72 2.1.2. Protecting the Access Token . . . . . . . . . . . . . 5 73 2.1.3. REGISTER Request . . . . . . . . . . . . . . . . . . 5 74 2.1.4. Non-REGISTER Request . . . . . . . . . . . . . . . . 5 75 2.2. UAS and Registrar Behavior . . . . . . . . . . . . . . . 6 76 2.3. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 6 77 3. Access Token Claims . . . . . . . . . . . . . . . . . . . . . 7 78 4. WWW-Authenticate Response Header Field . . . . . . . . . . . 7 79 5. Example Flows . . . . . . . . . . . . . . . . . . . . . . . . 8 80 5.1. Registration . . . . . . . . . . . . . . . . . . . . . . 8 81 5.2. Registration with Pre-Configured AS . . . . . . . . . . . 10 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 84 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 85 9. Normative References . . . . . . . . . . . . . . . . . . . . 12 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 88 1. Introduction 90 The Session Initiation Protocol (SIP) [RFC3261] uses the framework 91 used by HTTP [RFC7230] for authenticating users, which is a simple 92 challenge-response authentication mechanism that allows a server to 93 challenge a client request and allows a client to provide 94 authentication information in response to that challenge. 96 OAuth 2.0 [RFC6749] defines a token based authorization framework to 97 allow clients to access resources on behalf of their user. 99 The OpenID Connect 1.0 [OPENID] specifications defines a simple 100 identity layer on top of the OAuth 2.0 protocol, which enables 101 clients to verify the identity of the user based on the 102 authentication performed by a dedicated authorization server, as well 103 as to obtain basic profile information about the user. 105 This document updates [RFC3261], by defining the UAC procedures if it 106 receives a 401/407 response with multiple WWW-Authenticate/Proxy- 107 Authenticate header fields, providing challenges using different 108 authentication schemes for the same realm. 110 This document defines an mechanism for SIP, that relies on the OAuth 111 2.0 and OpenID Connect Core 1.0 specifications, to enable the 112 delegation of the user authentication and SIP registration 113 authorization to a dedicated third-party entity that is separate from 114 the SIP network elements that provide the SIP service. 116 1.1. Terminology 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in [RFC2119]. 122 1.2. SIP User Agent Types 124 [RFC6749] defines two types of clients, confidential and public, that 125 apply to the SIP User Agents. 127 * Confidential User Agent: is a SIP UA that is capable of 128 maintaining the confidentiality of the user credentials and any 129 tokens obtained using these user credentials. 131 * Public User Agent: is a SIP UA that is incapable of maintaining 132 the confidentiality of the user credentials and any obtained 133 tokens. 135 The mechanism defined in this document MUST only be used with 136 Confidential User Agents, as the UA is expected to obtain and 137 maintain tokens to be able to access the SIP network. 139 2. SIP Procedures 141 Section 22 of [RFC3261] defines the SIP procedures for the Digest 142 authentication mechanism procedures. The same procedures apply to 143 the Bearer authentication mechanism, with the changes described in 144 this section. 146 2.1. UAC Behavior 148 2.1.1. Obtaining Tokens 150 When a UAC sends a request without credentials (or with credentials 151 that are no longer valid), and receives a 401 (Unauthorized) or a 407 152 (Proxy Authentication Required) response that contains a WWW- 153 Authenticate header field (in case of a 401 response) or a Proxy- 154 Authenticate header field (in case of a 407 response) that indicates 155 "Bearer" scheme authentication and contains an address to an 156 Authorization Server, the UAC contacts the Authorization Server in 157 order to obtain tokens, and includes the requested scopes, based on a 158 local configuration. 160 The tokens returned to the UA depend on the type of AS: with an OAuth 161 AS, the tokens provided are the access token and refresh token. The 162 access token will be sent to the SIP servers to authorize UAC's 163 access to the service. The refresh token will only be used with the 164 AS to get new access token and refresh token, before the expiry of 165 the current access token. With an OpenID Connect server, an 166 additional ID-Token is returned, which contains the SIP URI and other 167 user specific details, and will be consumed by the UAC. 169 The detailed OAuth2 procedure to authenticate the user and obtain 170 these tokens is out of scope of this document. [RFC8252] defines 171 procedures for native applications. When using the mechanism defined 172 in [RFC8252] the user will be directed to use a browser for the 173 interaction with the authorization server, allowing the authorization 174 server to prompt the user for multi-factor authentication, redirect 175 the user to third-party identity providers, and the use of single- 176 sign-on sessions. 178 If the UAC receives a 401/407 response with multiple WWW- 179 Authenticate/Proxy-Authenticate header fields, providing challenges 180 using different authentication schemes for the same realm, the UAC 181 provides credentials for one or more of the schemes that it supports, 182 based on local policy. 184 NOTE: The address of the Authorization Server might be known to the 185 UAC e.g., using means of configuration, in which case the UAC can 186 contact the Authorization Server in order to obtain the access token 187 before it sends SIP request without credentials. 189 2.1.2. Protecting the Access Token 191 [RFC6749] mandates that Access Tokens are protected with TLS when in 192 transit. However, TLS only guarantees hop-to-hop protection when 193 used to protect SIP signaling. Therefore the Access Token MUST be 194 protected in a way so that only authorized SIP servers will have 195 access to it. Endpoints that support this specification MUST support 196 encrypted JSON Web Tokens (JWT) [RFC7519] for encoding and protecting 197 Access Token when included in SIP requests, unless some other 198 mechanism is used to guarantee that only authorized SIP endpoints 199 have access to the Access Token. 201 2.1.3. REGISTER Request 203 The procedures in this section assumes that the UAC has obtained a 204 token as specified in section Section 2.1.1 206 When the UAC sends a REGISTER request after it received a challenge 207 containing the Bearer scheme, then to resolve that particular 208 challenge it needs to send a request with an Authorization header 209 field containing the response to that challenge, including the Bearer 210 scheme carrying a valid access token in the request, as specified in 211 [RFC6750]. 213 Note that if there were multiple challenges with different schemes 214 then it maybe able to successfully retry the request using non-Bearer 215 credentials. 217 Based on local policy, the UAC MAY include an access token that has 218 been used for another binding associated with the same AOR in the 219 request. 221 If the access token included in a REGISTER request is not accepted, 222 and the UAC receives a 401 response or a 407 response, the UAC 223 follows the procedures in Section 2.1.1. 225 2.1.4. Non-REGISTER Request 227 The procedures in this section assumes that the UAC has obtained a 228 token as specified in section Section 2.1.1 229 When a UAC sends a request, after it received a challenge containing 230 the Bearer scheme, then the UAC MUST include an Authorization header 231 field with a Bearer scheme, carrying a valid access token in the 232 request, as specified in [RFC6750]. Based on local policy, the UAC 233 MAY include an access token that has been used for another dialog, or 234 for another stand-alone request, if the target of the new request is 235 the same. 237 If the access token included in a request is not accepted, and the 238 UAC receives a 401 response or a 407 response, the UAC follows the 239 procedures in Section 2.1.1. 241 2.2. UAS and Registrar Behavior 243 When a UAS or Registrar receives a request that fails to contain 244 authorization credentials acceptable to it, it SHOULD challenge the 245 request by sending a 401 (Unauthorized) response. To indicate that 246 it is willing to accept an OAuth2 token as a credential the UAS/ 247 Registrar MUST include a Proxy-Authentication header field in the 248 response, indicate "Bearer" scheme and include an address of an 249 Authorization Server from which the originator can obtain an access 250 token. 252 When a UAS/Registrar receives a SIP request that contains an 253 Authorization header field with an access token, the UAS/Registrar 254 MUST validate the access token, using the procedures associated with 255 the type of access token used, e.g. [RFC7519]. If the validation is 256 successful the UAS/Registrar can continue to process the request 257 using normal SIP procedures. If the validation fails, the UAS/ 258 Registrar MUST reject the request. 260 2.3. Proxy Behavior 262 When a proxy receives a request that fails to contain authorization 263 credentials acceptable to it, it SHOULD challenge the request by 264 sending a 407 (Proxy Authentication Required) response. To indicate 265 that it is willing to accept an OAuth2 token as a credential the 266 proxy MUST include a Proxy-Authentication header field in the 267 response, indicating "Bearer" scheme and including an address to an 268 Authorization Server from which the originator can obtain an access 269 token. 271 When a proxy wishes to authenticate a received request, it MUST 272 search the request for Proxy-Authorization header fields with 'realm' 273 parameters that match its realm. It then MUST successfully validate 274 the credentials from at least one Proxy-Authorization header field 275 for its realm. When the scheme is Bearer the proxy MUST validate the 276 access token, using the procedures associated with the type of access 277 token used, e.g. [RFC7519]. 279 3. Access Token Claims 281 The type of services that an access token grants access to can be 282 determined using different methods. Which methods are used and the 283 granted access provided by the token is based on local policy agreed 284 between the AS and the registrar. 286 If an access token is encoded as a JWT, it might contain a list of 287 claims [RFC7519], some registered and some are application specific 288 claims. The REGISTRAR can grant access to services either based on 289 such claims, using some other mechanism, or a combination of claims 290 and some other mechanism. If an access token is a reference token, 291 the REGISTRAR will grant access based on some other mechanism. 292 Examples of such other mechanisms are introspection [RFC7662], user 293 profile lookups, etc. 295 4. WWW-Authenticate Response Header Field 297 This section describes the syntax of the WWW-Authenticate Response 298 Header Field when used with the Bearer scheme to challenge the UA for 299 credentials, by extending the 'challnge' header field defined by 300 [RFC3261]. 302 challenge =/ ("Bearer" LWS bearer-cln *(COMMA bearer-cln)) 303 bearer-cln = realm / scope / authz-server / error / 304 auth-param 305 authz-server = "authz_server" EQUAL authz-server-value 306 authz-server-value = https-URI 307 realm = 308 auth-param = 309 scope = 310 error = 311 https-URI = 313 Figure 1: Bearer Scheme Syntax 315 The authz-server parameters contains the HTTPS URI, as defined in 316 [RFC7230], of the authorization server. The UA can discover metadata 317 about the AS using a mechanism like the one defined in [RFC8414]. 319 The realm and auth-param parameters are defined in [RFC3261]. 321 As per [RFC3261], the realm string alone defines the protection 322 domain. [RFC3261] states that the realm string must be globally 323 unique and recommends that the realm string contains a hostname or 324 domain name. It also states that the realm string should be human- 325 readable identifier that can be rendered to the user. 327 The scope and error parameters are defined in [RFC6749]. 329 The scope parameter could be used by the registrar/proxy to indicate 330 to the UAC the minimum scope that must be associated with the access 331 token to be able to get service. As defined in [RFC6749], the value 332 of the scope parameter is expressed as a list of space-delimited, 333 case-sensitive strings. The strings are defined by the authorization 334 server. The values of the scope parameter is out of scope of this 335 document. The UAC will use the scope provided by the registrar to 336 contact the AS and obtain a proper token with the requested scope. 338 The error parameter could be used by the registrar/proxy to indicate 339 to the UAC the reason for the error, with possible values of 340 "invalid_token" or "invalid_scope". 342 5. Example Flows 344 5.1. Registration 346 The figure below shows an example of a SIP registration, where the UA 347 is informed about the Authorization Server (AS) from where to obtain 348 an access token by the registratar in a 401 response to the REGISTER 349 request. 351 UA Registrar AS 352 --------------------------------------------------------------------- 353 | | | 354 | [1] REGISTER | | 355 |------------------------------>| | 356 | | | 357 | [2] 401 Unauthorized | | 358 | WWW-Authenticate: Bearer "authz_server"="" | 359 |<------------------------------| | 360 | | | 361 | [3] The UA interacts with the AS and obtains tokens, using | 362 | some out of scope mechanism. | 363 |<=============================================================>| 364 | | | 365 | [4] REGISTER | | 366 | Authorization: Bearer | 367 |------------------------------>| | 368 | | [5] HTTP POST /introspect | 369 | | {access_token} | 370 | |------------------------------>| 371 | | | 372 | | [6] 200 OK {metadata} | 373 | |<------------------------------| 374 | | | 375 | [7] 200 OK | | 376 |<------------------------------| | 377 | | | 379 Figure 2: Example Registration Flow 381 In step [1], the UA starts the registration process by sending a SIP 382 REGISTER request to the registrar without any credentials. 384 In step [2], the registrar challenges the UA, by sending a SIP 401 385 (Unauthorized) response to the REGISTER request. In the response the 386 registrar includes information about the AS to contact in order to 387 obtain a token. 389 In step [3], the UA interacts with the AS, potentially using the 390 OAuth Native App mechanism defined in [RFC8252], authenticates the 391 user and obtains the tokens needed to access the SIP service. 393 In step [4], the UA retries the registration process by sending a new 394 SIP REGISTER request that includes the access token that the UA 395 obtrained previously. 397 The registrar validates the access token. If the access token is a 398 reference token, the registrar MAY perform an introspection, as in 399 steps [5] and [6], in order to obtain more information about the 400 access token and its scope, as per [RFC7662]. Otherwise, after the 401 registrar validates the token to make sure it was signed by a trusted 402 entity, it inspects its claims and act upon it. 404 In step [7], once the registrar has succesfully verified and accepted 405 the access token, it sends a 200 (OK) response to the REGISTER 406 request. 408 5.2. Registration with Pre-Configured AS 410 The figure below shows an example of a SIP registration, where the UA 411 has pre-configured information about the Authorization Server (AS) 412 from where to obtain the access token. 414 UA Registrar AS 415 --------------------------------------------------------------------- 416 | | | 417 | [1] The UA interacts with the AS and obtains tokens, using | 418 | some out of scope mechanism. | 419 |<=============================================================>| 420 | | | 421 | [2] REGISTER | | 422 | Authorization: Bearer | 423 |------------------------------>| | 424 | | [3] HTTP POST /introspect | 425 | | {access_token} | 426 | |------------------------------>| 427 | | | 428 | | [4] 200 OK {metadata} | 429 | |<------------------------------| 430 | | | 431 | [5] 200 OK | | 432 |<------------------------------| | 433 | | | 435 Figure 3: Example Registration Flow - Authorization Server 436 Information Preconfigured 438 In step [1], the UA interacts with the AS, potentially using the 439 OAuth Native App mechanism defined in [RFC8252], authenticates the 440 user and obtains the tokens needed to access the SIP service. 442 In step [2], the UA retries the registration process by sending a new 443 SIP REGISTER request that includes the access token that the UA 444 obtrained previously. 446 The registrar validates the access token. If the access token is a 447 reference token, the registrar MAY perform an introspection, as in 448 steps [3] and [4], in order to obtain more information about the 449 access token and its scope, as per [RFC7662]. Otherwise, after the 450 registrar validates the token to make sure it was signed by a trusted 451 entity, it inspects its claims and act upon it. 453 In step [5], once the registrar has succesfully verified and accepted 454 the access token, it sends a 200 (OK) response to the REGISTER 455 request. 457 6. Security Considerations 459 The security considerations for OAuth are defined in [RFC6749]. The 460 security considerations for bearer tokens are defined in [RFC6750]. 461 The security considerations for JSON Web Tokens (JWT) are defined in 462 [RFC7519]. These security considerations also apply to SIP usage of 463 access token as defined in this document. 465 [RFC6749] mandates that Access Tokens are protected with TLS. 466 However, TLS only guarantees hop-to-hop protection when used to 467 protect SIP signaling. Therefore the Access Token MUST be protected 468 in a way so that only authorized SIP endpoints will have access to 469 it. Endpoints that support this specifications MUST support 470 encrypted JSON Web Tokens (JWT) [RFC7519] for encoding and protecting 471 Access Token when included in SIP requests, unless some other 472 mechanism is used to guarantee that only authorized SIP endpoints 473 have access to the Access Token. 475 7. IANA Considerations 477 8. Acknowledgments 479 The authors would like to specially thank Paul Kyzivat for his 480 multiple detailed reviews and suggested text that significanly 481 improved the quality of the document. 483 The authors would also like to thank the following for their review 484 and feedback on this document: 486 Olle Johansson, Roman Shpount, Dale Worley, and Jorgen Axell. 488 The authors would also like to thank the following for their review 489 and feedback of the original document that was replaced with this 490 document: 492 Andrew Allen, Martin Dolly, Keith Drage, Paul Kyzivat, Jon Peterson, 493 Michael Procter, Roy Radhika, Matt Ryan, Ivo Sedlacek, Roman Shpount, 494 Robert Sparks, Asveren Tolga, and Dale Worley. 496 The authors would also like to thank Jean Mahoney for her review, 497 editorial help, and the coversion of the XML source file from v2 to 498 v3. 500 9. Normative References 502 [OPENID] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and 503 C. Mortimore, "OpenID Connect Core 1.0", February 2014. 505 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 506 Requirement Levels", BCP 14, RFC 2119, 507 DOI 10.17487/RFC2119, March 1997, 508 . 510 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 511 A., Peterson, J., Sparks, R., Handley, M., and E. 512 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 513 DOI 10.17487/RFC3261, June 2002, 514 . 516 [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", 517 RFC 6749, DOI 10.17487/RFC6749, October 2012, 518 . 520 [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization 521 Framework: Bearer Token Usage", RFC 6750, 522 DOI 10.17487/RFC6750, October 2012, 523 . 525 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 526 Protocol (HTTP/1.1): Message Syntax and Routing", 527 RFC 7230, DOI 10.17487/RFC7230, June 2014, 528 . 530 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 531 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 532 . 534 [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", 535 RFC 7662, DOI 10.17487/RFC7662, October 2015, 536 . 538 [RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps", 539 BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017, 540 . 542 [RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 543 Authorization Server Metadata", RFC 8414, 544 DOI 10.17487/RFC8414, June 2018, 545 . 547 Authors' Addresses 549 Rifaat Shekh-Yusef 550 Avaya 551 425 Legget Drive 552 Ottawa Ontario 553 Canada 555 Phone: +1-613-595-9106 556 Email: rifaat.ietf@gmail.com 558 Christer Holmberg 559 Ericsson 560 Hirsalantie 11 561 FI- Jorvas 02420 562 Finland 564 Email: christer.holmberg@ericsson.com 566 Victor Pascual 567 webrtchacks 568 Spain 570 Email: victor.pascual.avila@gmail.com