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'BASIC' -- Obsolete informational reference (is this intentional?): RFC 2069 (Obsoleted by RFC 2617) -- Obsolete informational reference (is this intentional?): RFC 2818 (Obsoleted by RFC 9110) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 HTTPAuth Working Group R. Shekh-Yusef, Ed. 3 Internet-Draft D. Ahrens 4 Obsoletes: 2617 (if approved) Avaya 5 Intended Status: Standards Track S. Bremer 6 Expires: August 16, 2014 Netzkonform 7 February 12, 2014 9 HTTP Digest Access Authentication 10 draft-ietf-httpauth-digest-05 12 Abstract 14 HTTP provides a simple challenge-response authentication mechanism 15 that may be used by a server to challenge a client request and by a 16 client to provide authentication information. This document defines 17 the HTTP Digest Authentication scheme that may be used with the 18 authentication mechanism. 20 Status of this Memo 22 This Internet-Draft is submitted to IETF in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF), its areas, and its working groups. Note that 27 other groups may also distribute working documents as 28 Internet-Drafts. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 The list of current Internet-Drafts can be accessed at 36 http://www.ietf.org/1id-abstracts.html 38 The list of Internet-Draft Shadow Directories can be accessed at 39 http://www.ietf.org/shadow.html 41 Copyright and License Notice 43 Copyright (c) 2014 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 60 2 Syntax Convention . . . . . . . . . . . . . . . . . . . . . . . 4 61 2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 2.2 Algorithm Variants . . . . . . . . . . . . . . . . . . . . . 4 63 2.3 ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3 Digest Access Authentication Scheme . . . . . . . . . . . . . . 5 65 3.1 Overall Operation . . . . . . . . . . . . . . . . . . . . . 5 66 3.2 Representation of Digest Values . . . . . . . . . . . . . . 5 67 3.3 The WWW-Authenticate Response Header . . . . . . . . . . . . 5 68 3.4 The Authorization Request Header . . . . . . . . . . . . . . 8 69 3.4.1 Response . . . . . . . . . . . . . . . . . . . . . . . . 10 70 3.4.2 A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 71 3.4.3 A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 72 3.4.4 Username Hashing . . . . . . . . . . . . . . . . . . . . 11 73 3.4.5 Parameter Values and Quoted-String . . . . . . . . . . . 12 74 3.4.6 Various Considerations . . . . . . . . . . . . . . . . . 12 75 3.5 The Authentication-Info Header . . . . . . . . . . . . . . . 13 76 3.6 Digest Operation . . . . . . . . . . . . . . . . . . . . . . 15 77 3.7 Security Protocol Negotiation . . . . . . . . . . . . . . . 16 78 3.8 Proxy-Authenticate and Proxy-Authorization . . . . . . . . . 16 79 3.9 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17 80 3.9.1 Example with SHA-256 and MD5 . . . . . . . . . . . . . . 17 81 3.9.2 Example with SHA-512-256, Charset, and Userhash . . . . 18 82 4 Internationalization . . . . . . . . . . . . . . . . . . . . . . 20 83 5 Security Considerations . . . . . . . . . . . . . . . . . . . . 20 84 5.1 Limitations . . . . . . . . . . . . . . . . . . . . . . . . 20 85 5.2 Authentication of Clients using Digest Authentication . . . 21 86 5.3 Limited Use Nonce Values . . . . . . . . . . . . . . . . . . 21 87 5.4 Replay Attacks . . . . . . . . . . . . . . . . . . . . . . . 22 88 5.5 Weakness Created by Multiple Authentication Schemes . . . . 23 89 5.6 Online dictionary attacks . . . . . . . . . . . . . . . . . 23 90 5.7 Man in the Middle . . . . . . . . . . . . . . . . . . . . . 23 91 5.8 Chosen plaintext attacks . . . . . . . . . . . . . . . . . . 24 92 5.9 Precomputed dictionary attacks . . . . . . . . . . . . . . . 24 93 5.10 Batch brute force attacks . . . . . . . . . . . . . . . . . 25 94 5.11 Spoofing by Counterfeit Servers . . . . . . . . . . . . . . 25 95 5.12 Storing passwords . . . . . . . . . . . . . . . . . . . . . 25 96 5.13 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 26 97 6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 26 98 6.1 HTTP Digest Hash Algorithms Registry . . . . . . . . . . . 26 99 6.2 Digest Scheme Registration . . . . . . . . . . . . . . . . 27 100 6.3 Authentication-Info Header Registration . . . . . . . . . . 27 101 7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 28 102 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 103 8.1 Normative References . . . . . . . . . . . . . . . . . . . . 29 104 8.2 Informative References . . . . . . . . . . . . . . . . . . . 29 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 107 1 Introduction 109 HTTP provides a simple challenge-response authentication mechanism 110 that may be used by a server to challenge a client request and by a 111 client to provide authentication information. This document defines 112 the HTTP Digest Authentication scheme that may be used with the 113 authentication mechanism. 115 The details of the challenge-response authentication mechanism are 116 specified in the [HTTP-P7] document. 118 The combination of this document with Basic [BASIC] and [HTTP-P7] 119 obsolete RFC2617. 121 1.1 Terminology 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 125 document are to be interpreted as described in RFC 2119 [RFC2119]. 127 2 Syntax Convention 129 2.1 Examples 131 In the interest of clarity and readability, the extended parameters 132 or the headers and parameters in the examples in this document might 133 be broken into multiple lines. Any line that is indented in this 134 document is a continuation of the preceding line. 136 2.2 Algorithm Variants 138 When used with the Digest mechanism, each one of the algorithms has 139 two variants: Session variant and non-Session variant. 141 The non-Session variant is denoted by "", e.g. "SHA-256", 142 and the Session variant is denoted by "-sess", e.g. "SHA- 143 256-sess". 145 2.3 ABNF 147 This specification uses the Augmented Backus-Naur Form (ABNF) 148 notation of [RFC5234]. 150 3 Digest Access Authentication Scheme 152 3.1 Overall Operation 154 The Digest scheme is based on a simple challenge-response paradigm. 155 The Digest scheme challenges using a nonce value. A valid response 156 contains a checksum of the username, the password, the given nonce 157 value, the HTTP method, and the requested URI. In this way, the 158 password is never sent in the clear. The username and password must 159 be prearranged in some fashion not addressed by this document. 161 3.2 Representation of Digest Values 163 An optional header allows the server to specify the algorithm used to 164 create the checksum or digest. This documents adds SHA-256 and SHA- 165 512/256 algorithms. To maintain backwards compatibility, the MD5 166 algorithm is still supported but not recommended. 168 The size of the digest depends on the algorithm used. The bits in 169 the digest are converted from the most significant to the least 170 significant bit, four bits at a time to the ASCII representation as 171 follows. Each four bits is represented by its familiar hexadecimal 172 notation from the characters 0123456789abcdef, that is binary 0000 is 173 represented by the character '0', 0001 by '1' and so on up to the 174 representation of 1111 as 'f'. If the MD5 algorithm is used to 175 calculate the digest, then the digest will be represented as 32 176 hexadecimal characters, SHA-256 and SHA-512/256 by 64 hexadecimal 177 characters. 179 3.3 The WWW-Authenticate Response Header 181 If a server receives a request for an access-protected object, and an 182 acceptable Authorization header is not sent, the server responds with 183 a "401 Unauthorized" status code, and a WWW-Authenticate header with 184 Digest scheme as per the framework defined above, and include some or 185 all of the following parameters: 187 realm 188 A string to be displayed to users so they know which username and 189 password to use. This string should contain at least the name of 190 the host performing the authentication and might additionally 191 indicate the collection of users who might have access. An example 192 might be "registered_users@gotham.news.com". (See section 2.2 of 193 [HTTP-P7] for more details). 195 domain 196 A quoted, space-separated list of URIs, as specified in RFC 3986 197 [RFC3986], that define the protection space. If a URI is an 198 abs_path, it is relative to the canonical root URL of the server 199 being accessed. An absolute-URI in this list may refer to a 200 different server than the one being accessed. The client can use 201 this list to determine the set of URIs for which the same 202 authentication information may be sent: any URI that has a URI in 203 this list as a prefix (after both have been made absolute) may be 204 assumed to be in the same protection space. If this parameter is 205 omitted or its value is empty, the client should assume that the 206 protection space consists of all URIs on the responding server. 208 This parameter is not meaningful in Proxy-Authenticate headers, 209 for which the protection space is always the entire proxy; if 210 present it should be ignored. 212 nonce 213 A server-specified data string which should be uniquely generated 214 each time a 401 response is made. It is recommended that this 215 string be base64 or hexadecimal data. Specifically, since the 216 string is passed in the header lines as a quoted string, the 217 double-quote character is not allowed. 219 The contents of the nonce are implementation dependent. The 220 quality of the implementation depends on a good choice. A nonce 221 might, for example, be constructed as the base 64 encoding of 223 time-stamp H(time-stamp ":" ETag ":" private-key) 225 where time-stamp is a server-generated time or other non-repeating 226 value, ETag is the value of the HTTP ETag header associated with 227 the requested entity, and private-key is data known only to the 228 server. With a nonce of this form a server would recalculate the 229 hash portion after receiving the client authentication header and 230 reject the request if it did not match the nonce from that header 231 or if the time-stamp value is not recent enough. In this way the 232 server can limit the time of the nonce's validity. The inclusion 233 of the ETag prevents a replay request for an updated version of 234 the resource. (Note: including the IP address of the client in the 235 nonce would appear to offer the server the ability to limit the 236 reuse of the nonce to the same client that originally got it. 237 However, that would break proxy farms, where requests from a 238 single user often go through different proxies in the farm. Also, 239 IP address spoofing is not that hard.) 241 An implementation might choose not to accept a previously used 242 nonce or a previously used digest, in order to protect against a 243 replay attack. Or, an implementation might choose to use one-time 244 nonces or digests for POST or PUT requests and a time-stamp for 245 GET requests. For more details on the issues involved see section 246 5 of this document. 248 The nonce is opaque to the client. 250 opaque 251 A string of data, specified by the server, which should be 252 returned by the client unchanged in the Authorization header of 253 subsequent requests with URIs in the same protection space. It is 254 recommended that this string be base64 or hexadecimal data. 256 stale 257 A case-insensitive flag, indicating that the previous request from 258 the client was rejected because the nonce value was stale. If 259 stale is TRUE, the client may wish to simply retry the request 260 with a new encrypted response, without reprompting the user for a 261 new username and password. The server should only set stale to 262 TRUE if it receives a request for which the nonce is invalid but 263 with a valid digest for that nonce (indicating that the client 264 knows the correct username/password). If stale is FALSE, or 265 anything other than TRUE, or the stale parameter is not present, 266 the username and/or password are invalid, and new values must be 267 obtained. 269 algorithm 270 A string indicating a pair of algorithms used to produce the 271 digest and a checksum. If this is not present it is assumed to be 272 "MD5". If the algorithm is not understood, the challenge should be 273 ignored (and a different one used, if there is more than one). 275 In this document the string obtained by applying the digest 276 algorithm to the data "data" with secret "secret" will be denoted 277 by KD(secret, data), and the string obtained by applying the 278 checksum algorithm to the data "data" will be denoted H(data). The 279 notation unq(X) means the value of the quoted-string X without the 280 surrounding quotes. 282 For "" and "-sess" 284 H(data) = (data) 286 and 288 KD(secret, data) = H(concat(secret, ":", data)) 290 For example: 292 For the "SHA-256" and "SHA-256-sess" algorithms 294 H(data) = SHA-256(data) 296 i.e., the digest is the MD5 of the secret concatenated with a 297 colon concatenated with the data. The "MD5-sess" algorithm is 298 intended to allow efficient 3rd party authentication servers; 299 for the difference in usage, see the description in section 300 3.4.2. 302 qop 303 This parameter is optional, but is made so only for backward 304 compatibility with RFC 2069 [RFC2069]; it SHOULD be used by all 305 implementations compliant with this version of the Digest scheme. 306 If present, it is a quoted string of one or more tokens indicating 307 the "quality of protection" values supported by the server. The 308 value "auth" indicates authentication; the value "auth-int" 309 indicates authentication with integrity protection; see the 310 descriptions below for calculating the response parameter value 311 for the application of this choice. Unrecognized options MUST be 312 ignored. 314 charset 315 This is an optional parameter that is used by the server to 316 indicate the encoding scheme it supports. 318 userhash 319 This is an optional parameter that is used by the server to 320 indicate that it supports username hashing. Valid value are: 321 "true" or "false". 323 3.4 The Authorization Request Header 325 The client is expected to retry the request, passing an 326 Authorization header line with Digest scheme, which is defined 327 according to the framework above. The values of the opaque and 328 algorithm fields must be those supplied in the WWW-Authenticate 329 response header for the entity being requested. 331 The request includes some or all of the following parameters: 333 response 334 A string of the hex digits computed as defined below, which proves 335 that the user knows a password. 337 username 338 The user's name in the specified realm. 340 uri 341 The URI from request-target of the Request-Line; duplicated here 342 because proxies are allowed to change the Request-Line in transit. 344 qop 345 Indicates what "quality of protection" the client has applied to 346 the message. If present, its value MUST be one of the alternatives 347 the server indicated it supports in the WWW-Authenticate header. 348 These values affect the computation of the response. Note that 349 this is a single token, not a quoted list of alternatives as in 350 WWW-Authenticate. This parameter is optional in order to preserve 351 backward compatibility with a minimal implementation of RFC 2069 352 [RFC2069], but SHOULD be used if the server indicated that qop is 353 supported by providing a qop parameter in the WWW-Authenticate 354 header field. 356 cnonce 357 This MUST be specified if a qop parameter is sent (see above), and 358 MUST NOT be specified if the server did not send a qop parameter 359 in the WWW-Authenticate header field. The cnonce value is an 360 opaque quoted string value provided by the client and used by both 361 client and server to avoid chosen plaintext attacks, to provide 362 mutual authentication, and to provide some message integrity 363 protection. See the descriptions below of the calculation of the 364 rspauth and response values. 366 nc 367 The "nc" parameter stands for "nonce count". This MUST be 368 specified if a qop parameter is sent (see above), and MUST NOT be 369 specified if the server did not send a qop parameter in the WWW- 370 Authenticate header field. The nc value is the hexadecimal count 371 of the number of requests (including the current request) that the 372 client has sent with the nonce value in this request. For 373 example, in the first request sent in response to a given nonce 374 value, the client sends "nc=00000001". The purpose of this 375 parameter is to allow the server to detect request replays by 376 maintaining its own copy of this count - if the same nc value is 377 seen twice, then the request is a replay. See the description 378 below of the construction of the response value. 380 userhash 381 This optional parameter is used by the client to indicate that the 382 username has been hashed. Valid value are: "true" or "false". 384 If a parameter or its value is improper, or required parameters are 385 missing, the proper response is 400 Bad Request. If the request- 386 digest is invalid, then a login failure should be logged, since 387 repeated login failures from a single client may indicate an attacker 388 attempting to guess passwords. 390 The definition of response above indicates the encoding for its 391 value. The following definitions show how the value is computed. 393 3.4.1 Response 395 If the "qop" value is "auth" or "auth-int": 397 response = <"> < KD ( H(A1), unq(nonce) 398 ":" nc 399 ":" unq(cnonce) 400 ":" unq(qop) 401 ":" H(A2) 402 ) <"> 404 If the "qop" parameter is not present (this construction is for 405 compatibility with RFC 2069): 407 response = 408 <"> < KD ( H(A1), unq(nonce) ":" H(A2) ) > <"> 410 See below for the definitions for A1 and A2. 412 3.4.2 A1 414 If the "algorithm" parameter's value is "", e.g. "SHA- 415 256", then A1 is: 417 A1 = unq(username) ":" unq(realm) ":" passwd 419 where 421 passwd = < user's password > 423 If the "algorithm" parameter's value is "-sess", e.g. 424 "SHA-256-sess", then A1 is calculated only once - on the first 425 request by the client following receipt of a WWW-Authenticate 426 challenge from the server. It uses the server nonce from that 427 challenge, and the first client nonce value to construct A1 as 428 follows: 430 A1 = H( unq(username) ":" unq(realm) 431 ":" passwd ) 432 ":" unq(nonce) ":" unq(cnonce) 434 This creates a 'session key' for the authentication of subsequent 435 requests and responses which is different for each "authentication 436 session", thus limiting the amount of material hashed with any one 437 key. (Note: see further discussion of the authentication session in 438 section 3.6.) Because the server need only use the hash of the user 439 credentials in order to create the A1 value, this construction could 440 be used in conjunction with a third party authentication service so 441 that the web server would not need the actual password value. The 442 specification of such a protocol is beyond the scope of this 443 specification. 445 3.4.3 A2 447 If the "qop" parameter's value is "auth" or is unspecified, then A2 448 is: 450 A2 = Method ":" request-uri 452 If the "qop" value is "auth-int", then A2 is: 454 A2 = Method ":" request-uri ":" H(entity-body) 456 3.4.4 Username Hashing 458 To protect the transport of the username from the client to the 459 server, the server SHOULD set the "userhash" parameter with the value 460 of "true" in the WWW-Authentication header. 462 If the client supports the "userhash" parameter, and the "userhash" 463 parameter value in the WWW-Authentication header is set to "true", 464 then the client MUST calculate a hash of the username after any other 465 hash calculation and include the "userhash" parameter with the value 466 of "true" in the Authorization Request Header. If the client does not 467 provide the "username" as a hash value or the "userhash" parameter 468 with the value of "true", the server MAY reject the request. 470 The server may change the nonce value, so the client should be ready 471 to recalculate the hashed username. 473 The following is the operation that the client will take to hash the 474 username: 476 username = H( H( unq(username) ":" unq(realm) ) ":" unq(nonce) ) 478 3.4.5 Parameter Values and Quoted-String 480 Note that the value of many of the parameters, such as "username" 481 value, are defined as a "quoted-string". However, the "unq" notation 482 indicates that surrounding quotation marks are removed in forming the 483 string A1. Thus if the Authorization header includes the fields 485 username="Mufasa", realm=myhost@testrealm.com 487 and the user Mufasa has password "Circle Of Life" then H(A1) would be 488 H(Mufasa:myhost@testrealm.com:Circle Of Life) with no quotation marks 489 in the digested string. 491 No white space is allowed in any of the strings to which the digest 492 function H() is applied unless that white space exists in the quoted 493 strings or entity body whose contents make up the string to be 494 digested. For example, the string A1 illustrated above must be 496 Mufasa:myhost@testrealm.com:Circle Of Life 498 with no white space on either side of the colons, but with the white 499 space between the words used in the password value. Likewise, the 500 other strings digested by H() must not have white space on either 501 side of the colons which delimit their fields unless that white space 502 was in the quoted strings or entity body being digested. 504 Also note that if integrity protection is applied (qop=auth-int), the 505 H(entity-body) is the hash of the entity body, not the message body - 506 it is computed before any transfer encoding is applied by the sender 507 and after it has been removed by the recipient. Note that this 508 includes multipart boundaries and embedded headers in each part of 509 any multipart content-type. 511 3.4.6 Various Considerations 513 The "Method" value is the HTTP request method as specified in section 514 3.1.1 of [HTTP-P1]. The "request-target" value is the request-target 515 from the request line as specified in section 3.1.1 of [HTTP-P1]. 516 This may be "*", an "absolute-URI" or an "absolute-path" as specified 517 in section 2.7 of [HTTP-P1], but it MUST agree with the request- 518 target. In particular, it MUST be an "absolute-URI" if the request- 519 target is an "absolute-URI". The "cnonce" value is an optional 520 client-chosen value whose purpose is to foil chosen plaintext 521 attacks. 523 The authenticating server must assure that the resource designated by 524 the "uri" parameter is the same as the resource specified in the 525 Request-Line; if they are not, the server SHOULD return a 400 Bad 526 Request error. (Since this may be a symptom of an attack, server 527 implementers may want to consider logging such errors.) The purpose 528 of duplicating information from the request URL in this field is to 529 deal with the possibility that an intermediate proxy may alter the 530 client's Request-Line. This altered (but presumably semantically 531 equivalent) request would not result in the same digest as that 532 calculated by the client. 534 Implementers should be aware of how authenticated transactions 535 interact with shared caches. The HTTP/1.1 protocol specifies that 536 when a shared cache (see [HTTP-P6]) has received a request containing 537 an Authorization header and a response from relaying that request, it 538 MUST NOT return that response as a reply to any other request, unless 539 one of two Cache-Control (see section 3.2 of [HTTP-P6]) directive was 540 present in the response. If the original response included the "must- 541 revalidate" Cache-Control directive, the cache MAY use the entity of 542 that response in replying to a subsequent request, but MUST first 543 revalidate it with the origin server, using the request headers from 544 the new request to allow the origin server to authenticate the new 545 request. Alternatively, if the original response included the 546 "public" Cache-Control directive, the response entity MAY be returned 547 in reply to any subsequent request. 549 3.5 The Authentication-Info Header 551 The Authentication-Info header is used by the server to communicate 552 some information regarding the successful authentication in the 553 response. 555 Authentication-Info = auth-info 557 auth-info = *auth-param 559 The request includes some or all of the following parameters: 561 nextnonce 563 The value of the nextnonce parameter is the nonce the server 564 wishes the client to use for a future authentication response. 565 The server may send the Authentication-Info header with a 566 nextnonce field as a means of implementing one-time or otherwise 567 changing nonces. If the nextnonce field is present the client 568 SHOULD use it when constructing the Authorization header for its 569 next request. Failure of the client to do so may result in a 570 request to re-authenticate from the server with the "stale=TRUE". 572 Server implementations should carefully consider the 573 performance implications of the use of this mechanism; 574 pipelined requests will not be possible if every response 575 includes a nextnonce parameter that must be used on the next 576 request received by the server. Consideration should be given 577 to the performance vs. security tradeoffs of allowing an old 578 nonce value to be used for a limited time to permit request 579 pipelining. Use of the "nc" parameter can retain most of the 580 security advantages of a new server nonce without the 581 deleterious affects on pipelining. 583 qop 584 Indicates the "quality of protection" options applied to the 585 response by the server. The value "auth" indicates 586 authentication; the value "auth-int" indicates authentication with 587 integrity protection. The server SHOULD use the same value for the 588 qop parameter in the response as was sent by the client in the 589 corresponding request. 591 rspauth 593 The optional response digest in the "rspauth" parameter supports 594 mutual authentication -- the server proves that it knows the 595 user's secret, and with qop=auth-int also provides limited 596 integrity protection of the response. The "rspauth" value is 597 calculated as for the response in the Authorization header, except 598 that if "qop=auth" or is not specified in the Authorization header 599 for the request, A2 is 601 A2 = ":" request-uri 603 and if "qop=auth-int", then A2 is 605 A2 = ":" request-uri ":" H(entity-body) 607 cnonce and nc 609 The "cnonce" value and "nc" value MUST be the ones for the client 610 request to which this message is the response. The "rspauth", 611 "cnonce", and "nc" parameters MUST be present if "qop=auth" or 612 "qop=auth-int" is specified. 614 The Authentication-Info header is allowed in the trailer of an HTTP 615 message transferred via chunked transfer-coding. 617 3.6 Digest Operation 619 Upon receiving the Authorization header, the server may check its 620 validity by looking up the password that corresponds to the submitted 621 username. Then, the server must perform the same digest operation 622 (e.g., MD5) performed by the client, and compare the result to the 623 given response value. 625 Note that the HTTP server does not actually need to know the user's 626 cleartext password. As long as H(A1) is available to the server, the 627 validity of an Authorization header may be verified. 629 The client response to a WWW-Authenticate challenge for a protection 630 space starts an authentication session with that protection space. 631 The authentication session lasts until the client receives another 632 WWW-Authenticate challenge from any server in the protection space. A 633 client should remember the username, password, nonce, nonce count and 634 opaque values associated with an authentication session to use to 635 construct the Authorization header in future requests within that 636 protection space. The Authorization header may be included 637 preemptively; doing so improves server efficiency and avoids extra 638 round trips for authentication challenges. The server may choose to 639 accept the old Authorization header information, even though the 640 nonce value included might not be fresh. Alternatively, the server 641 may return a 401 response with a new nonce value, causing the client 642 to retry the request; by specifying stale=TRUE with this response, 643 the server tells the client to retry with the new nonce, but without 644 prompting for a new username and password. 646 Because the client is required to return the value of the opaque 647 parameter given to it by the server for the duration of a session, 648 the opaque data may be used to transport authentication session state 649 information. (Note that any such use can also be accomplished more 650 easily and safely by including the state in the nonce.) For example, 651 a server could be responsible for authenticating content that 652 actually sits on another server. It would achieve this by having the 653 first 401 response include a domain parameter whose value includes a 654 URI on the second server, and an opaque parameter whose value 655 contains the state information. The client will retry the request, at 656 which time the server might respond with a 301/302 redirection, 657 pointing to the URI on the second server. The client will follow the 658 redirection, and pass an Authorization header , including the 659 data. 661 As with the basic scheme, proxies must be completely transparent in 662 the Digest access authentication scheme. That is, they must forward 663 the WWW-Authenticate, Authentication-Info and Authorization headers 664 untouched. If a proxy wants to authenticate a client before a request 665 is forwarded to the server, it can be done using the Proxy- 666 Authenticate and Proxy-Authorization headers described in section 3.6 667 below. 669 3.7 Security Protocol Negotiation 671 It is useful for a server to be able to know which security schemes a 672 client is capable of handling. 674 It is possible that a server may want to require Digest as its 675 authentication method, even if the server does not know that the 676 client supports it. A client is encouraged to fail gracefully if the 677 server specifies only authentication schemes it cannot handle. 679 When a server receives a request to access a resource, the server 680 might challenge the client by responding with "401 Unauthorized" 681 status code, and include one or more WWW-Authenticate headers. If the 682 server challenges with multiple Digest headers, then each one of 683 these headers MUST use a different digest algorithm. The server MUST 684 add these Digest headers to the response in order of preference, 685 starting with the most preferred header, followed by the less 686 preferred headers. The preference of the algorithms is defined in the 687 IANA registry of the various algorithms as defined in section 6.1. 689 When the client receives the response it SHOULD use the topmost 690 header that it supports, unless a local policy dictates otherwise. 691 The client should ignore any challenge it does not understand. 693 3.8 Proxy-Authenticate and Proxy-Authorization 695 The digest authentication scheme may also be used for authenticating 696 users to proxies, proxies to proxies, or proxies to origin servers by 697 use of the Proxy-Authenticate and Proxy-Authorization headers. These 698 headers are instances of the Proxy-Authenticate and Proxy- 699 Authorization headers specified in sections 4.2 and 4.3 of the 700 HTTP/1.1 specification [HTTP-P7] and their behavior is subject to 701 restrictions described there. The transactions for proxy 702 authentication are very similar to those already described. Upon 703 receiving a request which requires authentication, the proxy/server 704 must issue the "407 Proxy Authentication Required" response with a 705 "Proxy-Authenticate" header. The digest-challenge used in the Proxy- 706 Authenticate header is the same as that for the WWW- Authenticate 707 header as defined above in section 3.2.1. 709 The client/proxy must then re-issue the request with a Proxy- 710 Authorization header, with parameters as specified for the 711 Authorization header in section 3.4 above. 713 On subsequent responses, the server sends Proxy-Authenticate-Info 714 with parameters the same as those for the Authentication-Info header 715 field. 717 Note that in principle a client could be asked to authenticate itself 718 to both a proxy and an end-server, but never in the same response. 720 3.9 Examples 722 3.9.1 Example with SHA-256 and MD5 724 The following example assumes that an access protected document is 725 being requested from the server via a GET request. The URI of the 726 document is http://www.nowhere.org/dir/index.html". Both client and 727 server know that the username for this document is "Mufasa" and the 728 password is "Circle of Life" ( with one space between each of the 729 three words). 731 The first time the client requests the document, no Authorization 732 header is sent, so the server responds with: 734 HTTP/1.1 401 Unauthorized 735 WWW-Authenticate: Digest 736 realm = "testrealm@host.com", 737 qop="auth, auth-int", 738 algorithm="SHA-256", 739 nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", 740 opaque="5ccc069c403ebaf9f0171e9517f40e41" 741 WWW-Authenticate: Digest 742 realm="testrealm@host.com", 743 qop="auth, auth-int", 744 algorithm="MD5", 745 nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", 746 opaque="5ccc069c403ebaf9f0171e9517f40ef41" 748 The client may prompt the user for their username and password, after 749 which it will respond with a new request, including the following 750 Authorization header if the client chooses MD5 digest: 752 Authorization:Digest username="Mufasa", 753 realm="testrealm@host.com", 754 nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", 755 uri="/dir/index.html", 756 qop="auth", 757 algorithm="MD5", 758 nc=00000001, 759 cnonce="0a4f113b", 760 response="6629fae49393a05397450978507c4ef1", 761 opaque="5ccc069c403ebaf9f0171e9517f40e41" 763 If the client chooses to use the SHA-256 algorithm for calculating 764 the response, the client responds with a new request including the 765 following Authorization header: 767 Authorization:Digest username="Mufasa", 768 realm="testrealm@host.com", 769 nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", 770 uri="/dir/index.html", 771 qop="auth", 772 algorithm="SHA-256", 773 nc=00000001, 774 cnonce="0a4f113b", 775 response="5abdd07184ba512a22c53f41470e5eea7dcaa3a93 776 a59b630c13dfe0a5dc6e38b", 777 opaque="5ccc069c403ebaf9f0171e9517f40e41" 779 3.9.2 Example with SHA-512-256, Charset, and Userhash 781 The following example assumes that an access protected document is 782 being requested from the server via a GET request. The URI for the 783 request is "http://api.example.org/doe.json". Both client and server 784 know the userhash of the username, support the UTF-8 charset, and use 785 the SHA-512-256 algorithm. The username for the request is "Jason 786 Doe" and the password is "Secret, or not?". 788 The first time the client requests the document, no Authorization 789 header is sent, so the server responds with: 791 HTTP/2.0 401 Unauthorized 792 WWW-Authenticate: Digest 793 realm="api@example.org", 794 qop=auth, 795 algorithm=SHA-512-256, 796 nonce="e145a96d70d40739596e60c6340f13be03290bd73c676d 797 3f25c01271af522eb2", 798 opaque="192cbcf2a2576846522c1a367c1dfdf0359a87719c5cc1 799 839e4f3d2ffeb82517", 800 charset=UTF-8, 801 userhash=true 803 The client may prompt the user for the required credentials and send 804 a new request with following Authorization header: 806 Authorization: Digest 807 username="298bc3decec198ec5e7ecc1d69f059ca33044dd15baf45 808 a1f87bbd7adb3784fd", 809 realm="api@example.org", 810 uri="/doe.json", 811 algorithm=SHA-512-256, 812 nonce="e145a96d70d40739596e60c6340f13be03290bd73c676d 813 3f25c01271af522eb2", 814 nc=00000001, 815 cnonce="cde966df34a49d5d842a263604159141c81db8d468e1bf 816 657230429424fc337a", 817 qop=auth, 818 response="ec180fc03b7a0dcd43c414f66f2335399bbe5f4d4ad469 819 f8233106ba453213c8", 820 opaque="192cbcf2a2576846522c1a367c1dfdf0359a87719c5cc1 821 839e4f3d2ffeb82517", 822 userhash=true 824 If the client can not provide a hashed username for any reason, the 825 client may try a request with this Authorization header: 827 Authorization: Digest 828 username="Jason Doe", 829 realm="api@example.org", 830 uri="/doe.json", 831 algorithm=SHA-512-256, 832 nonce="e145a96d70d40739596e60c6340f13be03290bd73c676d 833 3f25c01271af522eb2", 834 nc=00000001, 835 cnonce="cde966df34a49d5d842a263604159141c81db8d468e1bf 836 657230429424fc337a", 837 qop=auth, 838 response="ec180fc03b7a0dcd43c414f66f2335399bbe5f4d4ad469 839 f8233106ba453213c8", 840 opaque="192cbcf2a2576846522c1a367c1dfdf0359a87719c5cc1 841 839e4f3d2ffeb82517", 842 userhash=false 844 4 Internationalization 846 In challenges, servers SHOULD use the "charset" authentication 847 parameter (case-insensitive) to express the character encoding they 848 expect the user agent to use when generating A1 (see section 3.4.2) 849 and username hashing (see section 3.4.4). 851 The only allowed value is "UTF-8", to be matched case-insensitively, 852 indicating that the server expects the UTF-8 character encoding to be 853 used ([RFC3629]). 855 If the user agent does not support the encoding indicated by the 856 server, it MUST fail the request. 858 5 Security Considerations 860 5.1 Limitations 862 HTTP Digest authentication, when used with human-memorable passwords, 863 is vulnerable to dictionary attacks. Such attacks are much easier 864 than cryptographic attacks on any widely used algorithm, including 865 those that are no longer considered secure. In other words, algorithm 866 agility does not make this usage any more secure. 868 As a result, Digest authentication SHOULD be used only with passwords 869 that have a reasonable amount of entropy, e.g. 128-bit or more. Such 870 passwords typically cannot be memorized by humans but can be used for 871 automated web services. 873 Digest authentication SHOULD be used over a secure channel like HTTPS 874 [RFC2818]. 876 5.2 Authentication of Clients using Digest Authentication 878 Digest Authentication does not provide a strong authentication 879 mechanism, when compared to public key based mechanisms, for example. 881 However, it is significantly stronger than (e.g.) CRAM-MD5, which has 882 been proposed for use with LDAP [RFC4513], POP and IMAP (see 883 [RFC2195]). It is intended to replace the much weaker and even more 884 dangerous Basic mechanism. 886 Digest Authentication offers no confidentiality protection beyond 887 protecting the actual username and password. All of the rest of the 888 request and response are available to an eavesdropper. 890 Digest Authentication offers only limited integrity protection for 891 the messages in either direction. If qop=auth-int mechanism is used, 892 those parts of the message used in the calculation of the WWW- 893 Authenticate and Authorization header field response parameter values 894 (see section 3.2 above) are protected. Most header fields and their 895 values could be modified as a part of a man-in-the-middle attack. 897 Many needs for secure HTTP transactions cannot be met by Digest 898 Authentication. For those needs TLS or SHTTP are more appropriate 899 protocols. In particular Digest authentication cannot be used for any 900 transaction requiring confidentiality protection. Nevertheless many 901 functions remain for which Digest authentication is both useful and 902 appropriate. 904 5.3 Limited Use Nonce Values 906 The Digest scheme uses a server-specified nonce to seed the 907 generation of the response value (as specified in section 3.4.1 908 above). As shown in the example nonce in section 3.2.1, the server 909 is free to construct the nonce such that it may only be used from a 910 particular client, for a particular resource, for a limited period of 911 time or number of uses, or any other restrictions. Doing so 912 strengthens the protection provided against, for example, replay 913 attacks (see 4.5). However, it should be noted that the method 914 chosen for generating and checking the nonce also has performance and 915 resource implications. For example, a server may choose to allow 916 each nonce value to be used only once by maintaining a record of 917 whether or not each recently issued nonce has been returned and 918 sending a next-nonce parameter in the Authentication-Info header 919 field of every response. This protects against even an immediate 920 replay attack, but has a high cost checking nonce values, and perhaps 921 more important will cause authentication failures for any pipelined 922 requests (presumably returning a stale nonce indication). Similarly, 923 incorporating a request-specific element such as the Etag value for a 924 resource limits the use of the nonce to that version of the resource 925 and also defeats pipelining. Thus it may be useful to do so for 926 methods with side effects but have unacceptable performance for those 927 that do not. 929 5.4 Replay Attacks 931 A replay attack against Digest authentication would usually be 932 pointless for a simple GET request since an eavesdropper would 933 already have seen the only document he could obtain with a replay. 934 This is because the URI of the requested document is digested in the 935 client request and the server will only deliver that document. By 936 contrast under Basic Authentication once the eavesdropper has the 937 user's password, any document protected by that password is open to 938 him. 940 Thus, for some purposes, it is necessary to protect against replay 941 attacks. A good Digest implementation can do this in various ways. 942 The server created "nonce" value is implementation dependent, but if 943 it contains a digest of the client IP, a time-stamp, the resource 944 ETag, and a private server key (as recommended above) then a replay 945 attack is not simple. An attacker must convince the server that the 946 request is coming from a false IP address and must cause the server 947 to deliver the document to an IP address different from the address 948 to which it believes it is sending the document. An attack can only 949 succeed in the period before the time-stamp expires. Digesting the 950 client IP and time-stamp in the nonce permits an implementation which 951 does not maintain state between transactions. 953 For applications where no possibility of replay attack can be 954 tolerated the server can use one-time nonce values which will not be 955 honored for a second use. This requires the overhead of the server 957 remembering which nonce values have been used until the nonce time- 958 stamp (and hence the digest built with it) has expired, but it 959 effectively protects against replay attacks. 961 An implementation must give special attention to the possibility of 962 replay attacks with POST and PUT requests. Unless the server employs 963 one-time or otherwise limited-use nonces and/or insists on the use of 964 the integrity protection of qop=auth-int, an attacker could replay 965 valid credentials from a successful request with counterfeit form 966 data or other message body. Even with the use of integrity protection 967 most metadata in header fields is not protected. Proper nonce 968 generation and checking provides some protection against replay of 969 previously used valid credentials, but see 4.8. 971 5.5 Weakness Created by Multiple Authentication Schemes 973 An HTTP/1.1 server may return multiple challenges with a 401 974 (Authenticate) response, and each challenge may use a different auth- 975 scheme. A user agent MUST choose to use the strongest auth- scheme it 976 understands and request credentials from the user based upon that 977 challenge. 979 Note that many browsers will only recognize Basic and will require 980 that it be the first auth-scheme presented. Servers should only 981 include Basic if it is minimally acceptable. 983 When the server offers choices of authentication schemes using the 984 WWW-Authenticate header, the strength of the resulting authentication 985 is only as good as that of the of the weakest of the authentication 986 schemes. See section 5.7 below for discussion of particular attack 987 scenarios that exploit multiple authentication schemes. 989 5.6 Online dictionary attacks 991 If the attacker can eavesdrop, then it can test any overheard 992 nonce/response pairs against a list of common words. Such a list is 993 usually much smaller than the total number of possible passwords. The 994 cost of computing the response for each password on the list is paid 995 once for each challenge. 997 The server can mitigate this attack by not allowing users to select 998 passwords that are in a dictionary. 1000 5.7 Man in the Middle 1002 Both Basic and Digest authentication are vulnerable to "man in the 1003 middle" (MITM) attacks, for example, from a hostile or compromised 1004 proxy. Clearly, this would present all the problems of eavesdropping. 1005 But it also offers some additional opportunities to the attacker. 1007 A possible man-in-the-middle attack would be to add a weak 1008 authentication scheme to the set of choices, hoping that the client 1009 will use one that exposes the user's credentials (e.g. password). For 1010 this reason, the client should always use the strongest scheme that 1011 it understands from the choices offered. 1013 An even better MITM attack would be to remove all offered choices, 1014 replacing them with a challenge that requests only Basic 1015 authentication, then uses the cleartext credentials from the Basic 1016 authentication to authenticate to the origin server using the 1017 stronger scheme it requested. A particularly insidious way to mount 1018 such a MITM attack would be to offer a "free" proxy caching service 1019 to gullible users. 1021 User agents should consider measures such as presenting a visual 1022 indication at the time of the credentials request of what 1023 authentication scheme is to be used, or remembering the strongest 1024 authentication scheme ever requested by a server and produce a 1025 warning message before using a weaker one. It might also be a good 1026 idea for the user agent to be configured to demand Digest 1027 authentication in general, or from specific sites. 1029 Or, a hostile proxy might spoof the client into making a request the 1030 attacker wanted rather than one the client wanted. Of course, this is 1031 still much harder than a comparable attack against Basic 1032 Authentication. 1034 5.8 Chosen plaintext attacks 1036 With Digest authentication, a MITM or a malicious server can 1037 arbitrarily choose the nonce that the client will use to compute the 1038 response. This is called a "chosen plaintext" attack. The ability to 1039 choose the nonce is known to make cryptanalysis much easier. 1041 However, no way to analyze the MD5 one-way function used by Digest 1042 using chosen plaintext is currently known. 1044 The countermeasure against this attack is for clients to be 1045 configured to require the use of the optional "cnonce" parameter; 1046 this allows the client to vary the input to the hash in a way not 1047 chosen by the attacker. 1049 5.9 Precomputed dictionary attacks 1051 With Digest authentication, if the attacker can execute a chosen 1052 plaintext attack, the attacker can precompute the response for many 1053 common words to a nonce of its choice, and store a dictionary of 1054 (response, password) pairs. Such precomputation can often be done in 1055 parallel on many machines. It can then use the chosen plaintext 1056 attack to acquire a response corresponding to that challenge, and 1057 just look up the password in the dictionary. Even if most passwords 1058 are not in the dictionary, some might be. Since the attacker gets to 1059 pick the challenge, the cost of computing the response for each 1060 password on the list can be amortized over finding many passwords. A 1061 dictionary with 100 million password/response pairs would take about 1062 3.2 gigabytes of disk storage. 1064 The countermeasure against this attack is to for clients to be 1065 configured to require the use of the optional "cnonce" parameter. 1067 5.10 Batch brute force attacks 1069 With Digest authentication, a MITM can execute a chosen plaintext 1070 attack, and can gather responses from many users to the same nonce. 1071 It can then find all the passwords within any subset of password 1072 space that would generate one of the nonce/response pairs in a single 1073 pass over that space. It also reduces the time to find the first 1074 password by a factor equal to the number of nonce/response pairs 1075 gathered. This search of the password space can often be done in 1076 parallel on many machines, and even a single machine can search large 1077 subsets of the password space very quickly -- reports exist of 1078 searching all passwords with six or fewer letters in a few hours. 1080 The countermeasure against this attack is to for clients to be 1081 configured to require the use of the optional "cnonce" parameter. 1083 5.11 Spoofing by Counterfeit Servers 1085 Basic Authentication is vulnerable to spoofing by counterfeit 1086 servers. If a user can be led to believe that she is connecting to a 1087 host containing information protected by a password she knows, when 1088 in fact she is connecting to a hostile server, then the hostile 1089 server can request a password, store it away for later use, and feign 1090 an error. This type of attack is more difficult with Digest 1091 Authentication -- but the client must know to demand that Digest 1092 authentication be used, perhaps using some of the techniques 1093 described above to counter "man-in-the-middle" attacks. Again, the 1094 user can be helped in detecting this attack by a visual indication of 1095 the authentication mechanism in use with appropriate guidance in 1096 interpreting the implications of each scheme. 1098 5.12 Storing passwords 1100 Digest authentication requires that the authenticating agent (usually 1101 the server) store some data derived from the user's name and password 1102 in a "password file" associated with a given realm. Normally this 1103 might contain pairs consisting of username and H(A1), where H(A1) is 1104 the digested value of the username, realm, and password as described 1105 above. 1107 The security implications of this are that if this password file is 1108 compromised, then an attacker gains immediate access to documents on 1109 the server using this realm. Unlike, say a standard UNIX password 1110 file, this information need not be decrypted in order to access 1111 documents in the server realm associated with this file. On the other 1112 hand, decryption, or more likely a brute force attack, would be 1113 necessary to obtain the user's password. This is the reason that the 1114 realm is part of the digested data stored in the password file. It 1115 means that if one Digest authentication password file is compromised, 1116 it does not automatically compromise others with the same username 1117 and password (though it does expose them to brute force attack). 1119 There are two important security consequences of this. First the 1120 password file must be protected as if it contained unencrypted 1121 passwords, because for the purpose of accessing documents in its 1122 realm, it effectively does. 1124 A second consequence of this is that the realm string should be 1125 unique among all realms which any single user is likely to use. In 1126 particular a realm string should include the name of the host doing 1127 the authentication. The inability of the client to authenticate the 1128 server is a weakness of Digest Authentication. 1130 5.13 Summary 1132 By modern cryptographic standards Digest Authentication is weak. But 1133 for a large range of purposes it is valuable as a replacement for 1134 Basic Authentication. It remedies some, but not all, weaknesses of 1135 Basic Authentication. Its strength may vary depending on the 1136 implementation. In particular the structure of the nonce (which is 1137 dependent on the server implementation) may affect the ease of 1138 mounting a replay attack. A range of server options is appropriate 1139 since, for example, some implementations may be willing to accept the 1140 server overhead of one-time nonces or digests to eliminate the 1141 possibility of replay. Others may satisfied with a nonce like the one 1142 recommended above restricted to a single IP address and a single ETag 1143 or with a limited lifetime. 1145 The bottom line is that *any* compliant implementation will be 1146 relatively weak by cryptographic standards, but *any* compliant 1147 implementation will be far superior to Basic Authentication. 1149 6 IANA Considerations 1151 6.1 HTTP Digest Hash Algorithms Registry 1153 This specification creates a new IANA registry named "HTTP Digest 1154 Hash Algorithms". When registering a new hash algorithm, the 1155 following information MUST be provided: 1157 o Hash Algorithm 1158 The textual name of the hash algorithm. 1160 o Digest Size 1161 The size of the algorithm's output in hexadecimal characters. 1163 o Preference 1164 The preference of the algorithm, with 1.0 being the least 1165 preferred. This is a real number to allow for future algorithms 1166 to be added anywhere in the table. 1168 o Reference 1169 A reference to the specification that describes the new algorithm. 1171 The update policy for this registry shall be Specification Required. 1173 The initial registry will contain the following entries: 1175 Hash Algorithm Digest Size Preference Reference 1176 -------------- ----------- ---------- --------- 1177 "MD5" 32 1.0 RFC XXXX 1178 "SHA-512-256" 64 2.0 RFC XXXX 1179 "SHA-256" 64 3.0 RFC XXXX 1181 Each one of the algorithms defined in the registry might have a -sess 1182 variant, e.g. MD5-sess, SHA-256-sess, etc. 1184 6.2 Digest Scheme Registration 1186 This specification registers the Digest scheme with the 1187 Authentication Scheme Registry. 1189 Authentication Scheme Name: Digest 1191 Pointer to specification text: RFCXXX 1193 6.3 Authentication-Info Header Registration 1195 This specification registers the Authentication-Info Header with the 1196 Message Header Field Registry. 1198 Header Field Name: Authentication-Info 1199 Protocol: http 1201 Status: standard 1203 Reference: RFCXXXX, Section 3.5 1205 7 Acknowledgments 1207 The authors of this document would like to thank the authors of 1208 RFC2617, as this document heavily borrows text from their document to 1209 provide a complete description of the digest scheme and its 1210 operations. 1212 The authors would like to thank Stephen Farrell, Yoav Nir, Phillip 1213 Hallam-Baker, Manu Sporny, Paul Hoffman, Julian Reschke, Yaron 1214 Sheffer, Sean Turner, Geoff Baskwill, Eric Cooper, Bjoern Hoehrmann, 1215 Martin Durst, Peter Saint-Andre, Michael Sweet, Daniel Stenberg, and 1216 Brett Tate for their careful review and comments. 1218 The authors would like to thank Jonathan Stoke, Nico Williams, Harry 1219 Halpin, and Phil Hunt for their comments on the mailing list when 1220 discussing various aspects of this document. 1222 The authors would like to thank Paul Kyzivat and Dale Worley for 1223 their careful review and feedback on some aspects of this document. 1225 8 References 1227 8.1 Normative References 1229 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1230 Requirement Levels", BCP 14, RFC 2119, March 1997. 1232 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1233 10646", STD 63, RFC 3629, November 2003. 1235 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1236 Resource Identifier (URI): Generic Syntax", STD 66, 1237 RFC 3986, January 2005. 1239 [RFC4513] Harrison, R., Ed., "Lightweight Directory Access Protocol 1240 (LDAP): Authentication Methods and Security Mechanisms", 1241 RFC 4513, June 2006. 1243 [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for 1244 Syntax Specifications: ABNF", STD 68, RFC 5234, January 1245 2008. 1247 [HTTP-P1] Fielding, R., Reschke, J., "Hypertext Transfer Protocol 1248 (HTTP/1.1): Message Syntax and Routing", Work in Progress, 1249 November 2013. 1251 [HTTP-P6] Fielding, R., Nottingham, M., Reschke, J., "Hypertext 1252 Transfer Protocol (HTTP/1.1): Caching", Work in Progress, 1253 November 2013. 1255 [HTTP-P7] Fielding, R., Reschke, J., "Hypertext Transfer Protocol 1256 (HTTP/1.1): Authentication", Work in Progress, November 1257 2013. 1259 [BASIC] Reschke, J., "The 'Basic' HTTP Authentication Scheme", 1260 Work in Progress, September 2013. 1262 8.2 Informative References 1264 [RFC2069] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P., 1265 Luotonen, A., Sink, E., and L. Stewart, "An Extension to 1266 HTTP : Digest Access Authentication", RFC 2069, January 1267 1997. 1269 [RFC2195] Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP 1270 AUTHorize Extension for Simple Challenge/Response", 1271 RFC 2195, September 1997. 1273 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 1275 Authors' Addresses 1277 Rifaat Shekh-Yusef (Editor) 1278 Avaya 1279 250 Sydney Street 1280 Belleville, Ontario 1281 Canada 1283 Phone: +1-613-967-5267 1284 Email: rifaat.ietf@gmail.com 1286 David Ahrens 1287 Avaya 1288 California 1289 USA 1291 EMail: ahrensdc@gmail.com 1293 Sophie Bremer 1294 Netzkonform 1295 Germany 1297 Email: sophie.bremer@netzkonform.de