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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 KITTEN W. Mills 3 Internet-Draft Yahoo! Inc. 4 Intended status: Standards Track T. Showalter 5 Expires: August 18, 2014 6 H. Tschofenig 7 ARM Ltd. 8 February 14, 2014 10 A set of SASL Mechanisms for OAuth 11 draft-ietf-kitten-sasl-oauth-13.txt 13 Abstract 15 OAuth enables a third-party application to obtain limited access to a 16 protected resource, either on behalf of a resource owner by 17 orchestrating an approval interaction, or by allowing the third-party 18 application to obtain access on its own behalf. 20 This document defines how an application client uses credentials 21 obtained via OAuth over the Simple Authentication and Security Layer 22 (SASL) to access a protected resource at a resource serve. Thereby, 23 it enables schemes defined within the OAuth framework for non-HTTP- 24 based application protocols. 26 Clients typically store the user's long-term credential. This does, 27 however, lead to significant security vulnerabilities, for example, 28 when such a credential leaks. A significant benefit of OAuth for 29 usage in those clients is that the password is replaced by a shared 30 secret with higher entropy, i.e., the token. Tokens typically 31 provide limited access rights and can be managed and revoked 32 separately from the user's long-term password. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on August 18, 2014. 50 Copyright Notice 52 Copyright (c) 2014 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3. OAuth SASL Mechanism Specifications . . . . . . . . . . . . . 6 70 3.1. Initial Client Response . . . . . . . . . . . . . . . . . 7 71 3.1.1. Reserved Key/Values . . . . . . . . . . . . . . . . . 7 72 3.2. Server's Response . . . . . . . . . . . . . . . . . . . . 8 73 3.2.1. OAuth Identifiers in the SASL Context . . . . . . . . 8 74 3.2.2. Server Response to Failed Authentication . . . . . . 8 75 3.2.3. Completing an Error Message Sequence . . . . . . . . 9 76 3.3. OAuth Access Token Types using Keyed Message Digests . . 9 77 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 4.1. Successful Bearer Token Exchange . . . . . . . . . . . . 10 79 4.2. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 11 80 4.3. SMTP Example of a Failed Negotiation . . . . . . . . . . 12 81 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 82 6. Internationalization Considerations . . . . . . . . . . . . . 14 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 84 7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 14 85 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 86 8.1. Normative References . . . . . . . . . . . . . . . . . . 15 87 8.2. Informative References . . . . . . . . . . . . . . . . . 16 88 Appendix A. Acknowlegements . . . . . . . . . . . . . . . . . . 16 89 Appendix B. Document History . . . . . . . . . . . . . . . . . . 17 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 92 1. Introduction 94 OAuth 1.0a [RFC5849] and OAuth 2.0 [RFC6749] are protocol frameworks 95 that enable a third-party application to obtain limited access to a 96 protected resource, either on behalf of a resource owner by 97 orchestrating an approval interaction, or by allowing the third-party 98 application to obtain access on its own behalf. 100 The core OAuth 2.0 specification [RFC6749] specifies the interaction 101 between the OAuth client and the authorization server; it does not 102 define the interaction between the OAuth client and the resource 103 server for the access to a protected resource using an Access Token. 104 Instead, the OAuth client to resource server interaction is described 105 in separate specifications, such as the bearer token specification 106 [RFC6750] and the MAC Token specification 107 [I-D.ietf-oauth-v2-http-mac]. OAuth 1.0a included the protocol 108 specification for the communication between the OAuth client and the 109 resource server in [RFC5849]. 111 The main use cases for OAuth 2.0 and OAuth 1.0a have so far focused 112 on an HTTP-based environment only. This document integrates OAuth 113 1.0a and OAuth 2.0 into non-HTTP-based applications using the 114 integration into SASL. Hence, this document takes advantage of the 115 OAuth protocol and its deployment base to provide a way to use the 116 Simple Authentication and Security Layer (SASL) [RFC4422] to gain 117 access to resources when using non-HTTP-based protocols, such as the 118 Internet Message Access Protocol (IMAP) [RFC3501] and SMTP [RFC5321], 119 which is what this memo uses in the examples. 121 To illustrate the impact of integrating this specification into an 122 OAuth-enabled application environment Figure 1 shows the abstract 123 message flow of OAuth 2.0 [RFC6749]. As indicated in the figure, 124 this document impacts the exchange of messages (E) and (F) since SASL 125 is used for interaction between the client and the resource server 126 instead of HTTP. 128 ----+ 129 +--------+ +---------------+ | 130 | |--(A)-- Authorization Request --->| Resource | | 131 | | | Owner | |Plain 132 | |<-(B)------ Access Grant ---------| | |OAuth 133 | | +---------------+ |2.0 134 | | | 135 | | Client Credentials & +---------------+ | 136 | |--(C)------ Access Grant -------->| Authorization | | 137 | Client | | Server | | 138 | |<-(D)------ Access Token ---------| | | 139 | | (w/ Optional Refresh Token) +---------------+ | 140 | | ----+ 141 | | ----+ 142 | | +---------------+ | 143 | | | | |OAuth 144 | |--(E)------ Access Token -------->| Resource | |over 145 | | | Server | |SASL 146 | |<-(F)---- Protected Resource -----| | | 147 | | | | | 148 +--------+ +---------------+ | 149 ----+ 151 Figure 1: OAuth 2.0 Protocol Flow 153 The Simple Authentication and Security Layer (SASL) is a framework 154 for providing authentication and data security services in 155 connection-oriented protocols via replaceable authentication 156 mechanisms. It provides a structured interface between protocols and 157 mechanisms. The resulting framework allows new protocols to reuse 158 existing authentication protocols and allows old protocols to make 159 use of new authentication mechanisms. The framework also provides a 160 protocol for securing subsequent protocol exchanges within a data 161 security layer. 163 When OAuth is integrated into SASL the high-level steps are as 164 follows: 166 (A) The client requests authorization from the resource owner. 167 The authorization request can be made directly to the resource 168 owner (as shown), or preferably indirectly via the authorization 169 server as an intermediary. 171 (B) The client receives an authorization grant which is a 172 credential representing the resource owner's authorization, 173 expressed using one of four grant types defined in this 174 specification or using an extension grant type. The authorization 175 grant type depends on the method used by the client to request 176 authorization and the types supported by the authorization server. 178 (C) The client requests an access token by authenticating with the 179 authorization server and presenting the authorization grant. 181 (D) The authorization server authenticates the client and 182 validates the authorization grant, and if valid issues an access 183 token. 185 (E) The client requests the protected resource from the resource 186 server and authenticates by presenting the access token. 188 (F) The resource server validates the access token, and if valid, 189 indicates a successful authentication. 191 Again, steps (E) and (F) are not defined in [RFC6749] (but are 192 described in, for example, [RFC6750] for the OAuth Bearer Token 193 instead) and are the main functionality specified within this 194 document. Consequently, the message exchange shown in Figure 1 is 195 the result of this specification. The client will generally need to 196 determine the authentication endpoints (and perhaps the service 197 endpoints) before the OAuth 2.0 protocol exchange messages in steps 198 (A)-(D) are executed. The discovery of the resource owner and 199 authorization server endpoints is outside the scope of this 200 specification. The client must discover those endpoints using a 201 discovery mechanisms, such as Webfinger using host-meta [RFC7033]. 202 In band discovery is not tenable if clients support the OAuth 2.0 203 password grant. Once credentials are obtained the client proceeds to 204 steps (E) and (F) defined in this specification. 206 OAuth 1.0 follows a similar model but uses a different terminology 207 and does not separate the resource server from the authorization 208 server. 210 2. Terminology 212 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 213 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 214 document are to be interpreted as described in [RFC2119]. 216 The reader is assumed to be familiar with the terms used in the OAuth 217 2.0 specification [RFC6749]. 219 In examples, "C:" and "S:" indicate lines sent by the client and 220 server respectively. Line breaks have been inserted for readability. 222 Note that the IMAP SASL specification requires base64 encoding, see 223 Section 4 of [RFC4648], not this memo. 225 3. OAuth SASL Mechanism Specifications 227 SASL is used as an authentication framework in a variety of 228 application layer protocols. This document defines the following 229 SASL mechanisms for usage with OAuth: 231 OAUTHBEARER: OAuth 2.0 bearer tokens, as described in [RFC6750]. 232 RFC 6750 uses Transport Layer Security (TLS) to secure the 233 protocol interaction between the client and the resource 234 server. 236 OAUTH10A: OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed 237 message digest), as described in Section 3.4.2 of [RFC5849]. 239 New extensions may be defined to add additional OAuth Access Token 240 Types. Such a new SASL OAuth mechanism can be added by simply 241 registering the new name(s) and citing this specification for the 242 further definition. 244 These mechanisms are client initiated and lock-step, the server 245 always replying to a client message. In the case where the client 246 has and correctly uses a valid token the flow is: 248 o Client sends a valid and correct initial client response. 250 o Server responds with a successful authentication. 252 In the case where authorization fails the server sends an error 253 result, then client MUST then send an additional message to the 254 server in order to allow the server to finish the exchange. Some 255 protocols and common SASL implementations do not support both sending 256 a SASL message and finalizing a SASL negotiation, the additional 257 client message in the error case deals with this problem. This 258 exchange is: 260 o Client sends an invalid initial client response. 262 o Server responds with an error message. 264 o Client sends a dummy client response. 266 o Server fails the authentication. 268 3.1. Initial Client Response 270 Client responses are a key/value pair sequence. These key/value 271 pairs carry the equivalent values from an HTTP context in order to be 272 able to complete an OAuth style HTTP authorization. Unknown key/ 273 value pairs MUST be ignored by the server. The ABNF [RFC5234] syntax 274 is: 276 kvsep = %x01 277 key = 1*ALPHA 278 value = *(VCHAR / SP / HTAB / CR / LF ) 279 kvpair = key "=" value kvsep 280 client_resp = 0*kvpair kvsep 282 The following key/value pairs are defined in the client response: 284 auth (REQUIRED): The payload of the HTTP Authorization header for 285 an equivalent HTTP OAuth authorization. 287 host: Contains the host name to which the client connected. 289 port: Contains the port number represented as a decimal positive 290 integer string without leading zeros to which the client 291 connected. 293 qs: The HTTP query string. This is reserved for future use, the 294 client SHOUD NOT send it, and has the default value of "". 296 For OAuth token types that use keyed message digests the client MUST 297 send host and port number key/values, and the server MUST fail an 298 authorization request requiring keyed message digests that do not 299 have host and port values. In OAuth 1.0a for example, the so-called 300 "signature base string calculation" includes the reconstructed HTTP 301 URL. 303 3.1.1. Reserved Key/Values 305 In these mechanisms values for path, query string and post body are 306 assigned default values. OAuth authorization schemes MAY define 307 usage of these in the SASL context and extend this specification. 308 For OAuth Access Token Types that use request keyed message digest 309 the default values MUST be used unless explicit values are provided 310 in the client response. The following key values are reserved for 311 future use: 313 mthd (RESERVED): HTTP method, the default value is "POST". 315 path (RESERVED): HTTP path data, the default value is "/". 317 post (RESERVED): HTTP post data, the default value is "". 319 3.2. Server's Response 321 The server validates the response per the specification for the OAuth 322 Access Token Types used. If the OAuth Access Token Type utilizes a 323 keyed message digest of the request parameters then the client must 324 provide a client response that satisfies the data requirements for 325 the scheme in use. 327 The server responds to a successfully verified client message by 328 completing the SASL negotiation. The authenticated identity reported 329 by the SASL mechanism is the identity securely established for the 330 client with the OAuth credential. The application, not the SASL 331 mechanism, based on local access policy determines whether the 332 identity reported by the mechanism is allowed access to the requested 333 resource. Note that the semantics of the authz-id is specified by 334 the SASL framework [RFC4422]. 336 3.2.1. OAuth Identifiers in the SASL Context 338 In the OAuth framework the client may be authenticated by the 339 authorization server and the resource owner is authenticated to the 340 authorization server. OAuth access tokens may contain information 341 about the authentication of the resource owner and about the client 342 and may therefore make this information accessible to the resource 343 server. 345 If both identifiers are needed by an application the developer will 346 need to provide a way to communicate that from the SASL mechanism 347 back to the application. 349 3.2.2. Server Response to Failed Authentication 351 For a failed authentication the server returns a JSON [RFC4627] 352 formatted error result, and fails the authentication. The error 353 result consists of the following values: 355 status (REQUIRED): The authorization error code. Valid error 356 codes are defined in the IANA [[need registry name]] registry 357 specified in the OAuth 2 core specification. 359 scope (OPTIONAL): An OAuth scope which is valid to access the 360 service. This may be empty which implies that unscoped tokens 361 are required, or a space separated list. Use of a space 362 separated list is NOT RECOMMENDED. 364 If the resource server provides a scope then the client MUST always 365 request scoped tokens from the token endpoint. If the resource 366 server provides no scope to the client then the client SHOULD presume 367 an empty scope (unscoped token) is needed. 369 If channel binding is in use and the channel binding fails the server 370 responds with a status code set to 412 to indicate that the channel 371 binding precondition failed. If the authentication scheme in use 372 does not include signing the server SHOULD revoke the presented 373 credential and the client SHOULD discard that credential. 375 3.2.3. Completing an Error Message Sequence 377 Section 3.6 of [RFC4422] explicitly prohibits additional information 378 in an unsuccessful authentication outcome. Therefore, the error 379 message is sent in a normal message. The client MUST then send an 380 additional client response consisting of a single %x01 (control A) 381 character to the server in order to allow the server to finish the 382 exchange. 384 3.3. OAuth Access Token Types using Keyed Message Digests 386 OAuth Access Token Types may use keyed message digests and the client 387 and the resource server may need to perform a cryptographic 388 computation for integrity protection and data origin authentication. 390 OAuth is designed for access to resources identified by URIs. SASL 391 is designed for user authentication, and has no facility for more 392 fine-grained access control. In this specification we require or 393 define default values for the data elements from an HTTP request 394 which allow the signature base string to be constructed properly. 395 The default HTTP path is "/" and the default post body is empty. 396 These atoms are defined as extension points so that no changes are 397 needed if there is a revision of SASL which supports more specific 398 resource authorization, e.g., IMAP access to a specific folder or FTP 399 access limited to a specific directory. 401 Using the example in the OAuth 1.0a specification as a starting 402 point, on an IMAP server running on port 143 and given the OAuth 1.0a 403 style authorization request (with %x01 shown as ^A and line breaks 404 added for readability) below: 406 n,a=user@example.com^A 407 host=example.com^A 408 user=user@example.com^A 409 port=143^A 410 auth=OAuth realm="Example", 411 oauth_consumer_key="9djdj82h48djs9d2", 412 oauth_token="kkk9d7dh3k39sjv7", 413 oauth_signature_method="HMAC-SHA1", 414 oauth_timestamp="137131201", 415 oauth_nonce="7d8f3e4a", 416 oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A 418 The signature base string would be constructed per the OAuth 1.0 419 specification [RFC5849] with the following things noted: 421 o The method value is defaulted to POST. 423 o The scheme defaults to be "http", and any port number other than 424 80 is included. 426 o The path defaults to "/". 428 o The query string defaults to "". 430 In this example the signature base string with line breaks added for 431 readability would be: 433 POST&http%3A%2F%2Fexample.com:143%2F&oauth_consumer_key%3D9djdj82h4 434 8djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHMAC-SH 435 A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7 437 4. Examples 439 These examples illustrate exchanges between an IMAP and SMTP clients 440 and servers. 442 Note to implementers: The SASL OAuth method names are case 443 insensitive. One example uses "Bearer" but that could as easily be 444 "bearer", "BEARER", or "BeArEr". 446 4.1. Successful Bearer Token Exchange 448 This example shows a successful OAuth 2.0 bearer token exchange. 449 Note that line breaks are inserted for readability and the underlying 450 TLS establishment is not shown either. 452 S: * OK IMAP4rev1 Server Ready 453 C: t0 CAPABILITY 454 S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR 455 S: t0 OK Completed 456 C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX 457 J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV 458 GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE= 459 S: t1 OK SASL authentication succeeded 461 As required by IMAP [RFC3501], the payloads are base64-encoded. The 462 decoded initial client response (with %x01 represented as ^A and long 463 lines wrapped for readability) is: 465 n,a=user@example.com^Ahost=server.example.com^Aport=143^A 466 auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A 468 The same credential used in an SMTP exchange is shown below. Note 469 that line breaks are inserted for readability, and that the SMTP 470 protocol terminates lines with CR and LF characters (ASCII values 471 0x0D and 0x0A), these are not displayed explicitly in the example. 473 [connection begins] 474 S: 220 mx.example.com ESMTP 12sm2095603fks.9 475 C: EHLO sender.example.com 476 S: 250-mx.example.com at your service,[172.31.135.47] 477 S: 250-SIZE 35651584 478 S: 250-8BITMIME 479 S: 250-AUTH LOGIN PLAIN OAUTHBEARER 480 S: 250-ENHANCEDSTATUSCODES 481 S: 250 PIPELINING 482 C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX 483 J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV 484 GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE= 485 S: 235 Authentication successful. 486 [connection continues...] 488 4.2. Failed Exchange 490 This example shows a failed exchange because of the empty 491 Authorization header, which is how a client can query for the needed 492 scope. Note that line breaks are inserted for readability. 494 S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1 Server 495 Ready 496 S: t0 OK Completed 497 C: t1 AUTHENTICATE OAUTHBEARER cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcG 498 xlLmNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoP 499 QFjYmRhdGE9AQE= 500 S: + ewoic3RhdHVzIjoiNDAxIgoic2NvcGUiOiJleGFtcGxlX3Njb3BlIgp9 501 C: + AQ== 502 S: t1 NO SASL authentication failed 504 The decoded initial client response is: 506 n,a=user@example.com,^Ahost=server.example.com^A 507 port=143^Aauth=^A^A 509 The decoded server error response is: 511 { 512 "status":"401", 513 "scope":"example_scope" 514 } 516 The client responds with the required dummy response. 518 4.3. SMTP Example of a Failed Negotiation 520 This example shows an authorization failure in an SMTP exchange. 521 Note that line breaks are inserted for readability, and that the SMTP 522 protocol terminates lines with CR and LF characters (ASCII values 523 0x0D and 0x0A), these are not displayed explicitly in the example. 525 [connection begins] 526 S: 220 mx.example.com ESMTP 12sm2095603fks.9 527 C: EHLO sender.example.com 528 S: 250-mx.example.com at your service,[172.31.135.47] 529 S: 250-SIZE 35651584 530 S: 250-8BITMIME 531 S: 250-AUTH LOGIN PLAIN OAUTHBEARER 532 S: 250-ENHANCEDSTATUSCODES 533 S: 250 PIPELINING 534 C: AUTH OAUTHBEARER bixhPT1zb21ldXNlckBleGFtcGxlLmNvbQFhdXRoPUJlYXJlciB2 535 RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ== 536 S: 334 eyJzdGF0dXMiOiI0MDEiLCJzY2hlbWVzIjoiYmVhcmVyIG1hYyIsInNjb3BlIjoia 537 HR0cHM6Ly9tYWlsLmdvb2dsZS5jb20vIn0K 538 C: AQ== 539 S: 535-5.7.1 Username and Password not accepted. Learn more at 540 S: 535 5.7.1 http://support.example.com/mail/oauth 541 [connection continues...] 542 The server returned an error message in the 334 SASL message, the 543 client responds with the required dummy response, and the server 544 finalizes the negotiation. 546 5. Security Considerations 548 OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios, 549 and the security properties of these profiles vary. As shown in 550 Figure 1 this specification is aimed to be integrated into a larger 551 OAuth deployment. Application developers therefore need to 552 understand the needs of their security requirements based on a threat 553 assessment before selecting a specific SASL OAuth mechanism. For 554 OAuth 2.0 a detailed security document [RFC6819] provides guidance to 555 select those OAuth 2.0 components that help to mitigate threats for a 556 given deployment. For OAuth 1.0a Section 4 of RFC 5849 [RFC5849] 557 provides guidance specific to OAuth 1.0. 559 This document specifies three SASL Mechanisms for OAuth and each 560 comes with different security properties. 562 OAUTHBEARER: This mechanism borrows from OAuth 2.0 bearer tokens 563 [RFC6750]. It relies on the application using TLS to protect the 564 OAuth 2.0 Bearer Token exchange; without TLS usage at the 565 application layer this method is completely insecure. 566 Consequently, TLS MUST be provided by the application when 567 choosing this authentication mechanism. 569 OAUTH10A: This mechanism re-uses OAuth 1.0a MAC tokens (using the 570 HMAC-SHA1 keyed message digest), as described in Section 3.4.2 of 571 [RFC5849]. To compute the keyed message digest in the same way 572 was in RFC 5839 this specification conveys additional parameters 573 between the client and the server. This SASL mechanism only 574 supports client authentication. If server-side authentication is 575 desireable then it must be provided by the application underneath 576 the SASL layer. The use of TLS is strongly RECOMMENDED. 578 Additionally, the following aspects are worth pointing out: 580 An access token is not equivalent to the user's long term password. 582 Care has to be taken when these OAuth credentials are used for 583 actions like changing passwords (as it is possible with some 584 protocols, e.g., XMPP). The resource server should ensure that 585 actions taken in the authenticated channel are appropriate to the 586 strength of the presented credential. 588 Lifetime of the appliation sessions. 590 It is possible that SASL will be authenticating a connection and 591 the life of that connection may outlast the life of the access 592 token used to establish it. This is a common problem in 593 application protocols where connections are long-lived, and not a 594 problem with this mechanism per se. Resource servers may 595 unilaterally disconnect clients in accordance with the application 596 protocol. 598 Access tokens have a lifetime. 600 Reducing the lifetime of an access token provides security 601 benefits and OAuth 2.0 introduces refresh tokens to obtain new 602 access token on the fly without any need for a human interaction. 603 Additionally, a previously obtained access token may be revoked or 604 rendered invalid at any time by the authorization server. The 605 client may request a new access token for each connection to a 606 resource server, but it should cache and re-use valid credentials. 608 6. Internationalization Considerations 610 The identifer asserted by the OAuth authorization server about the 611 resource owner inside the access token may be displayed to a human. 612 For example, when SASL is used in the context of IMAP the resource 613 server may assert the resource owner's email address to the IMAP 614 server for usage in an email-based application. The identifier may 615 therefore contain internationalized characters and an application 616 needs to ensure that the mapping between the identifier provided by 617 OAuth is suitable for use with the application layer protocol SASL is 618 incorporated into. 620 At the time of writing the standardization of the various claims in 621 the access token (in JSON format) is still ongoing, see 622 [I-D.ietf-oauth-json-web-token]. Once completed it will provide a 623 standardized format for exchanging identity information between the 624 authorization server and the resource server. 626 7. IANA Considerations 628 7.1. SASL Registration 630 The IANA is requested to register the following SASL profile: 632 SASL mechanism profile: OAUTHBEARER 634 Security Considerations: See this document 636 Published Specification: See this document 637 For further information: Contact the authors of this document. 639 Owner/Change controller: the IETF 641 Note: None 643 The IANA is requested to register the following SASL profile: 645 SASL mechanism profile: OAUTH10A 647 Security Considerations: See this document 649 Published Specification: See this document 651 For further information: Contact the authors of this document. 653 Owner/Change controller: the IETF 655 Note: None 657 8. References 659 8.1. Normative References 661 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 662 Requirement Levels", BCP 14, RFC 2119, March 1997. 664 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 665 (SHA1)", RFC 3174, September 2001. 667 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 668 Security Layer (SASL)", RFC 4422, June 2006. 670 [RFC4627] Crockford, D., "The application/json Media Type for 671 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 673 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 674 Encodings", RFC 4648, October 2006. 676 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 677 Channels", RFC 5056, November 2007. 679 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 680 Specifications: ABNF", STD 68, RFC 5234, January 2008. 682 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 683 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 685 [RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849, 686 April 2010. 688 [RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 689 6749, October 2012. 691 [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization 692 Framework: Bearer Token Usage", RFC 6750, October 2012. 694 8.2. Informative References 696 [I-D.ietf-oauth-json-web-token] 697 Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 698 (JWT)", draft-ietf-oauth-json-web-token-15 (work in 699 progress), January 2014. 701 [I-D.ietf-oauth-v2-http-mac] 702 Richer, J., Mills, W., Tschofenig, H., and P. Hunt, "OAuth 703 2.0 Message Authentication Code (MAC) Tokens", draft-ietf- 704 oauth-v2-http-mac-05 (work in progress), January 2014. 706 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 707 4rev1", RFC 3501, March 2003. 709 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 710 October 2008. 712 [RFC6819] Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0 713 Threat Model and Security Considerations", RFC 6819, 714 January 2013. 716 [RFC7033] Jones, P., Salgueiro, G., Jones, M., and J. Smarr, 717 "WebFinger", RFC 7033, September 2013. 719 Appendix A. Acknowlegements 721 The authors would like to thank the members of the Kitten working 722 group, and in addition and specifically: Simon Josefson, Torsten 723 Lodderstadt, Ryan Troll, Alexey Melnikov, Jeffrey Hutzelman, and Nico 724 Williams. 726 This document was produced under the chairmanship of Alexey Melnikov, 727 Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman. The supervising area 728 directors was Stephen Farrell. 730 Appendix B. Document History 732 [[ to be removed by RFC editor before publication as an RFC ]] 734 -13 736 o Changed affiliation. 738 -12 740 o Removed -PLUS components from the specification. 742 -11 744 o Removed GSS-API components from the specification. 746 o Updated security consideration section. 748 -10 750 o Clarifications throughout the document in response to the feedback 751 from Jeffrey Hutzelman. 753 -09 755 o Incorporated review by Alexey and Hannes. 757 o Clarified the three OAuth SASL mechanisms. 759 o Updated references 761 o Extended acknowledgements 763 -08 765 o Fixed the channel binding examples for p=$cbtype 767 o More tuning of the authcid language and edited and renamed 3.2.1. 769 -07 771 o Struck the MUST langiage from authzid. 773 o 775 -06 777 o Removed the user field. Fixed the examples again. 779 o Added canonicalization language. 781 o 783 -05 785 o Fixed the GS2 header language again. 787 o Separated out different OAuth schemes into different SASL 788 mechanisms. Took out the scheme in the error return. Tuned up 789 the IANA registrations. 791 o Added the user field back into the SASL message. 793 o Fixed the examples (again). 795 o 797 -04 799 o Changed user field to be carried in the gs2-header, and made gs2 800 header explicit in all cases. 802 o Converted MAC examples to OAuth 1.0a. Moved MAC to an informative 803 reference. 805 o Changed to sending an empty client response (single control-A) as 806 the second message of a failed sequence. 808 o Fixed channel binding prose to refer to the normative specs and 809 removed the hashing of large channel binding data, which brought 810 mroe problems than it solved. 812 o Added a SMTP examples for Bearer use case. 814 -03 816 o Added user field into examples and fixed egregious errors there as 817 well. 819 o Added text reminding developers that Authorization scheme names 820 are case insensitive. 822 -02 824 o Added the user data element back in. 826 o Minor editorial changes. 828 -01 830 o Ripping out discovery. Changed to refer to I-D.jones-appsawg- 831 webfinger instead of WF and SWD older drafts. 833 o Replacing HTTP as the message format and adjusted all examples. 835 -00 837 o Renamed draft into proper IETF naming format now that it's 838 adopted. 840 o Minor fixes. 842 Authors' Addresses 844 William Mills 845 Yahoo! Inc. 847 Email: wmills_92105@yahoo.com 849 Tim Showalter 851 Email: tjs@psaux.com 853 Hannes Tschofenig 854 ARM Ltd. 855 110 Fulbourn Rd 856 Cambridge CB1 9NJ 857 Great Britain 859 Email: Hannes.tschofenig@gmx.net 860 URI: http://www.tschofenig.priv.at