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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Lear 3 Internet-Draft Cisco Systems GmbH 4 Intended status: Standards Track H. Tschofenig 5 Expires: February 14, 2011 Nokia Siemens Networks 6 H. Mauldin 7 Cisco Systems, Inc. 8 S. Josefsson 9 SJD AB 10 August 13, 2010 12 A SASL & GSS-API Mechanism for OpenID 13 draft-ietf-kitten-sasl-openid-00 15 Abstract 17 OpenID has found its usage on the Internet for Web Single Sign-On. 18 Simple Authentication and Security Layer (SASL) and the Generic 19 Security Service Application Program Interface (GSS-API) are 20 application frameworks to generalize authentication. This memo 21 specifies a SASL and GSS-API mechanism for OpenID that allows the 22 integration of existing OpenID Identity Providers with applications 23 using SASL and GSS-API. 25 Status of this Memo 27 This Internet-Draft is submitted to IETF in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF), its areas, and its working groups. Note that 32 other groups may also distribute working documents as Internet- 33 Drafts. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 The list of current Internet-Drafts can be accessed at 41 http://www.ietf.org/ietf/1id-abstracts.txt. 43 The list of Internet-Draft Shadow Directories can be accessed at 44 http://www.ietf.org/shadow.html. 46 This Internet-Draft will expire on February 14, 2011. 48 Copyright Notice 49 Copyright (c) 2010 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 66 1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 67 2. Applicability for non-HTTP Use Cases . . . . . . . . . . . . . 5 68 2.1. Binding SASL to OpenID in the Relying Party . . . . . . . 8 69 2.2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 8 70 3. OpenID SASL Mechanism Specification . . . . . . . . . . . . . 10 71 3.1. Advertisement . . . . . . . . . . . . . . . . . . . . . . 10 72 3.2. Initiation . . . . . . . . . . . . . . . . . . . . . . . . 10 73 3.3. Authentication Request . . . . . . . . . . . . . . . . . . 10 74 3.4. Server Response . . . . . . . . . . . . . . . . . . . . . 11 75 4. OpenID GSS-API Mechanism Specification . . . . . . . . . . . . 12 76 4.1. GSS-API Principal Name Types for OpenID . . . . . . . . . 12 77 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 78 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15 79 6.1. Binding OpenIDs to Authorization Identities . . . . . . . 15 80 6.2. RP redirected by malicious URL to take an improper 81 action . . . . . . . . . . . . . . . . . . . . . . . . . . 15 82 6.3. Session Swapping (Cross-Site Request Forgery) . . . . . . 15 83 6.4. User Privacy . . . . . . . . . . . . . . . . . . . . . . . 16 84 6.5. Collusion between RPs . . . . . . . . . . . . . . . . . . 16 85 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 86 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 87 9. Normative References . . . . . . . . . . . . . . . . . . . . . 19 88 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 20 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 91 1. Introduction 93 OpenID [OpenID] is a three-party protocol that provides a means for a 94 user to offer identity assertions and other attributes to a web 95 server (Relying Party) via the help of an identity provider. The 96 purpose of this system is to provide a way to verify that an end user 97 controls an identifier. 99 Simple Authentication and Security Layer (SASL) [RFC4422] (SASL) is 100 used by application protocols such IMAP, POP and XMPP, with the goal 101 of modularizing authentication and security layers, so that newer 102 mechanisms can be added as needed. This memo specifies just such a 103 mechanism. 105 The Generic Security Service Application Program Interface (GSS-API) 106 [RFC2743] provides a framework for applications to support multiple 107 authentication mechanisms through a unified interface. This document 108 defines a pure SASL mechanism for OpenID, but it conforms to the new 109 bridge between SASL and the GSS-API called GS2 [I-D.ietf-sasl-gs2]. 110 This means that this document defines both a SASL mechanism and a 111 GSS-API mechanism. We want to point out that the GSS-API interface 112 is optional for SASL implementers, and the GSS-API considerations can 113 be avoided in environments that uses SASL directly without GSS-API. 115 As currently envisioned, this mechanism is to allow the interworking 116 between SASL and OpenID in order to assert identity and other 117 attributes to relying parties. As such, while servers (as relying 118 parties) will advertise SASL mechanisms, clients will select the 119 OpenID mechanism. 121 The OpenID mechanism described in this memo aims to re-use the 122 available OpenID specification to a maximum extent and therefore does 123 not establish a separate authentication, integrity and 124 confidentiality mechanism. It is anticipated that existing security 125 layers, such as Transport Layer Security (TLS), will continued to be 126 used. 128 Figure 1 describes the interworking between OpenID and SASL. This 129 document requires enhancements to the Relying Party and to the Client 130 (as the two SASL communication end points) but no changes to the 131 OpenID Provider (OP) are necessary. To accomplish this goal indirect 132 messaging required by the OpenID specification is tunneled within 133 SASL. 135 +-----------+ 136 | | 137 >| Relying | 138 / | Party | 139 // | | 140 // +-----------+ 141 // ^ 142 OpenID // +--|--+ 143 // | O| | 144 / S | p| | 145 // A | e| | 146 // S | n| | 147 // L | I| | 148 // | D| | 149 | Client | 154 | | | | 155 +------------+ +----------+ 157 Figure 1: Interworking Architecture 159 1.1. Terminology 161 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 162 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 163 document are to be interpreted as described in RFC 2119 [RFC2119]. 165 The reader is assumed to be familiar with the terms used in the 166 OpenID 2.0 specification. 168 1.2. Applicability 170 Because this mechanism transports information that should not be 171 controlled by an attacker, the OpenID mechanism MUST only be used 172 over channels protected by TLS [RFC5246], and the client MUST 173 successfully validate the server certificate, or similar integrity 174 protected and authenticated channels. 176 2. Applicability for non-HTTP Use Cases 178 OpenID was originally envisioned for HTTP/HTML based communications, 179 and with the associated semantic, the idea being that the user would 180 be redirected by the Relying Party to an identity provider who 181 authenticates the user, and then sends identity information and other 182 attributes (either directly or indirectly) to the Relying Party. The 183 identity provider in the OpenID specifications is referred to as an 184 OpenID Provider (OP). The actual protocol flow, as copied from the 185 OpenID 2.0 specification, is as follows: 187 1. The end user initiates authentication by presenting a User- 188 Supplied Identifier to the Relying Party via their User-Agent 189 (e.g., http://user.example.com). 191 2. After normalizing the User-Supplied Identifier, the Relying Party 192 performs discovery on it and establishes the OP Endpoint URL that 193 the end user uses for authentication. It should be noted that 194 the User-Supplied Identifier may be an OP Identifier, which 195 allows selection of a Claimed Identifier at the OP or for the 196 protocol to proceed without a Claimed Identifier if something 197 else useful is being done via an extension. 199 3. The Relying Party and the OP optionally establish an association 200 -- a shared secret established using Diffie-Hellman Key Exchange. 201 The OP uses an association to sign subsequent messages and the 202 Relying Party to verify those messages; this removes the need for 203 subsequent direct requests to verify the signature after each 204 authentication request/response. 206 4. The Relying Party redirects the end user's User-Agent to the OP 207 with an OpenID Authentication request. This occurs as stated in 208 Section 10.3 of [RFC2616]. 210 5. The OP authenticates the end user and establishes whether the end 211 user will authenticate to, and share specific attributes with, 212 the Relying Party. For instance, the OP often asks the user what 213 to do. The manner in which the end user authenticates to their 214 OP and any policies surrounding such authentication is out of 215 scope of OpenID. 217 6. The OP redirects the end user's User-Agent back to the Relying 218 Party with either an assertion that authentication is approved or 219 a message that authentication failed. 221 7. The Relying Party verifies the information received from the OP 222 including checking the Return URL, verifying the discovered 223 information, checking the nonce, and verifying the signature by 224 using either the shared key established during the association or 225 by sending a direct request to the OP. 227 When considering this flow in the context of SASL, we note that while 228 the RP and the client both must change their code to implement this 229 SASL mechanism, it is a design constraint that the OP behavior remain 230 untouched, in order for implementations to interoperate with existing 231 IdPs. Hence, an analog flow that interfaces the three parties needs 232 to be created. In the analog, we note that unlike a web server, the 233 SASL server already has some sort of session (probably a TCP 234 connection) established with the client. However, it may be 235 necessary to redirect a SASL client to another application. This 236 will be discussed below. By doing so, we externalize much of the 237 authentiction from SASL. 239 The steps are shown from below: 241 1. The Relying Party or SASL server advertises support for the SASL 242 OpenID mechanism to the client. 244 2. The client initiates a SASL authentiation and transmits the 245 User-Supplied Identifier as well as an optional return_to 246 parameter. 248 3. After normalizing the User-Supplied Identifier, the Relying 249 Party performs discovery on it and establishes the OP Endpoint 250 URL that the end user uses for authentication. 252 4. The Relying Party and the OP optionally establish an association 253 -- a shared secret established using Diffie-Hellman Key 254 Exchange. The OP uses an association to sign subsequent 255 messages and the Relying Party to verify those messages; this 256 removes the need for subsequent direct requests to verify the 257 signature after each authentication request/response. 259 5. The Relying Party transmits an authentication request to the OP 260 to obtain an assertion in the form of an indirect request. 261 These messages are passed through the client rather than 262 directly between the RP and the OP. OpenID defines two methods 263 for indirect communication, namely HTTP redirects and HTML form 264 submission. Both mechanisms are not directly applicable for 265 usage with SASL. To ensure that a standard OpenID 2.0 capable 266 OP can be used a new method is defined in this document that 267 requires the OpenID message content to be encoded using a 268 Universal Resource Idenitifier (URI). [RFC3986] 270 6. The SASL client now sends an empty response, as authentication 271 continues via the normal OpenID flow. 273 7. At this point the client application MUST construct a URL 274 containing the content received in the previous message from the 275 RP. This URL is transmitted to the OP either by the SASL client 276 application or an appropriate handler, such as a browser. 278 8. Next the client optionally authenticates to the OP and then 279 approves or disapproves authentication to the Relying Party. 280 The manner in which the end user is authenticated to their 281 respective OP and any policies surrounding such authentication 282 is out of scope of OpenID and and hence also out of scope for 283 this specification. This step happens out of band from SASL. 285 9. The OP will convey information about the success or failure of 286 the authentication phase back to the RP, again using an indirect 287 response via the client browser or handler. The client 288 transmits over HTTP the redirect of the OP result to the RP. 289 This step happens out of band from SASL. 291 10. The RP MAY send an OpenID check_authentication request directly 292 to the OP, if no association has been established, and the OP 293 should be expected to respond. Again this step happens out of 294 band from SASL. 296 11. The SASL server sends an appropriate SASL response to the 297 client, with optional Open Simple Registry (SREG) attributes. 299 SASL Serv. Client OP 300 |>-----(1)----->| | Advertisement 301 | | | 302 |<-----(2)-----<| | Initiation 303 | | | 304 |> - - (3) - - - - - - - - - ->| Discovery 305 | | 306 |>- - -(4)- - - - - - - - - - >| Association 307 |<- - -(4)- - - - - - - - - - <| 308 | | | 309 |>-----(5)----->| | Indirect Auth Request 310 | | | 311 |<-----(6)-----<| | Client Empty Response 312 | | | 313 | |>- - (7)- - ->| Client GET to the OP (ext) 314 | | | 315 | |<- - (8)- - ->| Client / OP Auth. (ext.) 316 | | | 317 |<- - -(9)- - - + - - - - - - <| HTTP(s) Indirect id_res 318 | | | 319 |<- - -(10)- - - - - - - - - ->| Optional check_authenticate 320 | | | 321 |>-----(11)---->| | SASL completion with status 323 ----- = SASL 324 - - - = HTTP or SSL 326 Note the directionality in SASL is such that the client MUST send an 327 empty response. Specifically, it processes the redirect and then 328 awaits a final SASL decision, while the rest of the OpenID 329 authentication process continues. 331 2.1. Binding SASL to OpenID in the Relying Party 333 To ensure that a specific request is bound, and in particular to ease 334 interprocess communication, it may be necessary for the relying party 335 to encode some sort of nonce in the URIs it transmits through the 336 client for success or failure. This can be done in any number of 337 ways. Examples would include making changes to the base URI or 338 otherwise including an additional fragment. 340 2.2. Discussion 342 As mentioned above OpenID is primarily designed to interact with web- 343 based applications. Portions of the authentication stream are only 344 defined in the crudest sense. That is, when one is prompted to 345 approve or disapprove an authentication, anything that one might find 346 on a browser is allowed, including JavaScript, fancy style-sheets, 347 etc. Because of this lack of structure, implementations will need to 348 invoke a fairly rich browser in order to insure that the 349 authentication can be completed. 351 Once there is an outcome, the SASL server needs to know about it. 352 The astute will hopefully by now have noticed an empty client SASL 353 challenge. This is not to say that nothing is happening, but rather 354 that authentication flow has shifted from SASL to OpenID, and will 355 return when the server has an outcome to hand to the client. The 356 alternative to this flow is some signal from the HTML browser to the 357 SASL client of the results that is in turn passed to the SASL server. 358 The IPC issue this raises is substantial. Better, we conclude, to 359 externalize the authentication to the browser, and have an empty 360 client challenge. 362 3. OpenID SASL Mechanism Specification 364 Based on the previous figure, the following operations are performed 365 with the OpenId SASL mechanism: 367 3.1. Advertisement 369 To advertise that a server supports OpenID, during application 370 session initiation, it displays the name "OPENID20" in the list of 371 supported SASL mechanisms. 373 3.2. Initiation 375 A client initiates an OpenID authentication with SASL by sending the 376 GS2 header followed by the XRI or URI, as specified in the OpenID 377 specification. The GS2 header carries the optional authorization 378 identity. 380 initial-response = gs2-header Auth-Identifier 381 Auth-Identifier = Identifier ; authentication identifier 382 Identifier = URI | XRI ; Identifer is specified in 383 ; Sec. 7.2 of the OpenID 2.0 spec. 385 The "gs2-header" is specified in [I-D.ietf-sasl-gs2], and it is used 386 as follows. The "gs2-nonstd-flag" MUST NOT be present. The "gs2-cb- 387 flag" MUST be "n" because channel binding is not supported by this 388 mechanism. The "gs2-authzid" carries the optional authorization 389 identity. 391 The XRI syntax is defined in [XRI2.0]. URI is specified in 392 [RFC3986]. 394 3.3. Authentication Request 396 The SASL Server sends an OpenID message that contains an openid.mode 397 of either "checkid_immediate" or "checkid_setup", as specified in 398 Section 9.1 of the OpenID 2.0 specification. 400 The client now sends that request via an HTTP GET to the OP, as if 401 redirected to do so from an HTTP server. 403 The client MUST handle both user authentication to the OP and 404 confirmation or rejection of the authentiation of the RP. 406 After all authentication has been completed by the OP, and after the 407 response has been sent to the client, the client will relay the 408 response to the Relying Party via HTTP or SSL. 410 3.4. Server Response 412 The Relying Party now validates the response it received from the 413 client via HTTP or SSL, as specified in the OpenID specification. 415 The response by the Relying Party consists of an application specific 416 response code indicating success or failure of authentication. In 417 the additional data, the server MAY include OpenID Simple Registry 418 (SREG) attributes that are listed in Section 4 of [SREG1.0]. They 419 are encoded as follows: 421 1. Strip "openid.sreg." from each attribute name. 423 2. Treat the concatentation of results as URI parameters that are 424 separated by an ambersand (&) and encode as one would a URI, 425 absent the scheme, authority, and the question mark. 427 For example: email=lear@example.com&fullname=Eliot%20Lear 429 More formally: 431 outcome_data = [ sreg_avp *( "," sreg_avp ) ] 432 sreg_avp = sreg_attr "=" sreg_val 433 sreg_attr = sreg_word 434 sreg_val = sreg_word 435 sreg_word = 1* ( unreserved / pct-encoded ) 436 ; pct-encoded from Section 2.1 of RFC 3896 437 ; unreserved from Section 2.3 of RFC 3896 439 If the application protocol allows, openid.error and 440 openid.error_code and any other useful diagnostic information SHOULD 441 be included in authentication failures. 443 4. OpenID GSS-API Mechanism Specification 445 This section and its sub-sections and all normative references of it 446 not referenced elsewhere in this document are INFORMATIONAL for SASL 447 implementors, but they are NORMATIVE for GSS-API implementors. 449 The OpenID SASL mechanism is actually also a GSS-API mechanism. The 450 messages are the same, but a) the GS2 header on the client's first 451 message and channel binding data is excluded when OpenID is used as a 452 GSS-API mechanism, and b) the RFC2743 section 3.1 initial context 453 token header is prefixed to the client's first authentication message 454 (context token). 456 The GSS-API mechanism OID for OpenID is 1.3.6.1.4.1.11591.4.5. 458 OpenID security contexts always have the mutual_state flag 459 (GSS_C_MUTUAL_FLAG) set to TRUE. OpenID does not support credential 460 delegation, therefore OpenID security contexts alway have the 461 deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE. 463 The OpenID mechanism does not support per-message tokens or 464 GSS_Pseudo_random. 466 4.1. GSS-API Principal Name Types for OpenID 468 OpenID supports standard generic name syntaxes for acceptors such as 469 GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). 471 OpenID supports only a single name type for initiators: 472 GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type for 473 OpenID. 475 OpenID name normalization is covered by the OpenID specification, see 476 [OpenID] section 7.2. 478 The query, display, and exported name syntaxes for OpenID principal 479 names are all the same. There are no OpenID-specific name syntaxes 480 -- applications should use generic GSS-API name types such as 481 GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], 482 Section 4). The exported name token does, of course, conform to 483 [RFC2743], Section 3.2, but the "NAME" part of the token should be 484 treated as a potential input string to the OpenID name normalization 485 rules. 487 GSS-API name attributes may be defined in the future to hold the 488 normalized OpenID Identifier. 490 5. Example 492 Suppose one has an OpenID of http://openid.example, and wishes to 493 authenticate his IMAP connection to mail.example (where .example is 494 the top level domain specified in [RFC2606]). The user would input 495 his Openid into his mail user agent, when he configures the account. 496 In this case, no association is attempted between the OpenID Consumer 497 and the OP. The client will make use of the return_to attribute to 498 capture results of the authentication to be redirected to the server. 499 The authentication on the wire would then look something like the 500 following: 502 (S = IMAP server; C = IMAP client) 504 C: < connects to IMAP port> 505 S: * OK 506 C: C1 CAPABILITY 507 S: * CAPABILITY IMAP4rev1 SASL-IR SORT [...] AUTH=OPENID20 508 S: C1 OK Capability Completed 509 C: C2 AUTHENTICATE OPENID biwsaHR0cDovL29wZW5pZC5leGFtcGxlLw== 510 [ This is the base64 encoding of "n,,http://openid.example/". 511 Server performs discovery on http://openid.example/ ] 512 S: + aHR0cDovL29wZW5pZC5leGFtcGxlL29wZW5pZC8/b3BlbmlkLm5z 513 PWh0dHA6Ly9zcGVjcy5vcGVuaWQubmV0L2F1dGgvMi4wJm9wZW5p 514 ZC5yZXR1cm5fdG89aHR0cHM6Ly9tYWlsLmV4YW1wbGUvY29uc3Vt 515 ZXIvMWVmODg4YyZvcGVuaWQuY2xhaW1lZF9pZD1odHRwczovL29w 516 ZW5pZC5leGFtcGxlLyZvcGVuaWQuaWRlbnRpdHk9aHR0cHM6Ly9v 517 cGVuaWQuZXhhbXBsZS8mb3BlbmlkLnJlYWxtPWltYXA6Ly9tYWls 518 LmV4YW1wbGUmb3BlbmlkLm1vZGU9Y2hlY2tpZF9zZXR1cA== 519 [ This is the base64 encoding of "http://openid.example/openid/ 520 ?openid.ns=http://specs.openid.net/auth/2.0 521 &openid.return_to=https://mail.example/consumer/1ef888c 522 &openid.claimed_id=https://openid.example/ 523 &openid.identity=https://openid.example/ 524 &openid.realm=imap://mail.example 525 &openid.mode=checkid_setup" 526 with line breaks and spaces added here for readibility. 527 ] 528 C: 529 [ The client now sends the URL it received to a browser for 530 processing. The user logs into http://openid.example, and 531 agrees to authenticate imap://mail.example. A redirect is 532 passed back to the client browser who then connects to 533 https://imap.example/consumer via SSL with the results. 534 From an IMAP perspective, however, the client sends an empty 535 response, and awaits mail.example. 536 Server mail.example would now contact openid.example with an 537 openid.check_authenticate message. After that... 538 ] 539 S: + ZW1haWw9bGVhckBtYWlsLmV4YW1wbGUsZnVsbG5hbWU9RWxp 540 b3QlMjBMZWFy 541 [ Here the IMAP server has returned an SREG attribute of 542 email=lear@mail.example,fullname=Eliot%20Lear. 543 Line break added in this example for clarity. ] 544 C: 545 [ In IMAP client must send a blank response to receive data 546 that is included in a success response. ] 547 S: C2 OK 549 6. Security Considerations 551 This section will address only security considerations associated 552 with the use of OpenID with SASL applications. For considerations 553 relating to OpenID in general, the reader is referred to the OpenID 554 specification and to other literature. Similarly, for general SASL 555 Security Considerations, the reader is referred to that 556 specification. 558 6.1. Binding OpenIDs to Authorization Identities 560 As specified in [RFC4422], the server is responsible for binding 561 credentials to a specific authorization identity. It is therefore 562 necessary that either some sort of registration process takes place 563 to register specific OpenIDs, or that only specific trusted OpenID 564 Providers be allowed. Some out of band knowledge may help this 565 process along. For instance, users of a particular domain may 566 utilize a particular OP that enforces a mapping. 568 6.2. RP redirected by malicious URL to take an improper action 570 In the initial SASL client response a user or host can transmit a 571 malicious response to the RP for purposes of taking advantage of 572 weaknesses in the RP's OpenID implementation. It is possible to add 573 port numbers to the URL so that the outcome is the RP does a port 574 scan of the site. The URL could send the connection to an internal 575 host or even the local host, which the attacker would not normally 576 have access to. The URL could contain a protocol other than http or 577 https, such as file or ftp. 579 To mitigate this attack, implementations should carefully analyze 580 URLs received, eliminating any that would in some way be privileged. 581 A log of those sites that fail SHOULD be kept, and limitations on 582 queries from clients should be imposed, just as with any other 583 authentication attempt. 585 6.3. Session Swapping (Cross-Site Request Forgery) 587 There is no defined mechanism in the OpenID protocol to bind the 588 OpenID session to the user's browser. An attacker may forge a cross- 589 site request in the log-in form, which has the user logging into a 590 proper RP as the attacker. The user would not recognize they are 591 logged into the site as the attacker, and so may reveal information 592 at the RP. Cross-site request forgery is a widely exploited 593 vulnerability at web sites. This is only concern in the context SASL 594 in as much as the client is not configured with the Relying Party 595 (e.g., SASL server) in a safe manner. 597 6.4. User Privacy 599 The OP is aware of each RP that a user logs into. There is nothing 600 in the protocol to hide this information from the OP. It is not a 601 requirement to track the visits, but there is nothing that prohibits 602 the collection of information. SASL servers should be aware that 603 OpenID Providers will be track - to some extent - user access to 604 their services and any additional information that OP provides. 606 6.5. Collusion between RPs 608 It is possible for RPs to link data that they have collected on you. 609 By using the same identifier to log into every RP, collusion between 610 RPs is possible. In OpenID 2.0, directed identity was introduced. 611 Directed identity allows the OP to transform the identifier the user 612 typed in to another identifier. This way the RP would never see the 613 actual user identifier, but a randomly generated identifier. This is 614 an option the user has to understand and decide to use if the OP is 615 supporting it. 617 7. IANA Considerations 619 The IANA is requested to register the following SASL profile: 621 SASL mechanism profile: OPENID20 623 Security Considerations: See this document 625 Published Specification: See this document 627 For further information: Contact the authors of this document. 629 Owner/Change controller: the IETF 631 Note: None 633 8. Acknowledgments 635 The authors would like to thank Alexey Melenkov, Joe Hildebrand, Mark 636 Crispin, Chris Newman, Leif Johansson, and Klaas Wierenga for their 637 review and contributions. 639 9. Normative References 641 [I-D.ietf-sasl-gs2] 642 Josefsson, S. and N. Williams, "Using GSS-API Mechanisms 643 in SASL: The GS2 Mechanism Family", draft-ietf-sasl-gs2-20 644 (work in progress), January 2010. 646 [OpenID] OpenID Foundation, "OpenID Authentication 2.0 - Final", 647 December 2007. 649 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 650 Requirement Levels", BCP 14, RFC 2119, March 1997. 652 [RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS 653 Names", BCP 32, RFC 2606, June 1999. 655 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 656 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 657 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 659 [RFC2743] Linn, J., "Generic Security Service Application Program 660 Interface Version 2, Update 1", RFC 2743, January 2000. 662 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 663 Resource Identifier (URI): Generic Syntax", STD 66, 664 RFC 3986, January 2005. 666 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 667 Security Layer (SASL)", RFC 4422, June 2006. 669 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 670 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 672 [SREG1.0] OpenID Foundation, "OpenID Simple Registration Extension 673 version 1.0", June 2006. 675 [XRI2.0] Reed, D. and D. McAlpin, "Extensible Resource Identifier 676 (XRI) Syntax V2.0", OASIS Standard xri-syntax-V2.0-cs, 677 September 2005. 679 Appendix A. Changes 681 This section to be removed prior to publication. 683 o 00 WG -00 draft. Slight wording modifications abou design 684 constraints per Alexey. 686 o 02 Correct single (significant) error on mechanism name. 688 o 01 Add nonce discussion, add authorized identity, explain a 689 definition. Add gs2 support. 691 o 00 Initial Revision. 693 Authors' Addresses 695 Eliot Lear 696 Cisco Systems GmbH 697 Richtistrasse 7 698 Wallisellen, ZH CH-8304 699 Switzerland 701 Phone: +41 44 878 9200 702 Email: lear@cisco.com 704 Hannes Tschofenig 705 Nokia Siemens Networks 706 Linnoitustie 6 707 Espoo 02600 708 Finland 710 Phone: +358 (50) 4871445 711 Email: Hannes.Tschofenig@gmx.net 712 URI: http://www.tschofenig.priv.at 714 Henry Mauldin 715 Cisco Systems, Inc. 716 170 West Tasman Drive 717 San Jose, CA 95134 718 USA 720 Phone: +1 (800) 553-6387 721 Email: hmauldin@cisco.com 723 Simon Josefsson 724 SJD AB 725 Hagagatan 24 726 Stockholm 113 47 727 SE 729 Email: simon@josefsson.org 730 URI: http://josefsson.org/