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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 HTTPAuth Working Group J. Reschke 3 Internet-Draft greenbytes 4 Obsoletes: 2617 (if approved) December 19, 2014 5 Intended status: Standards Track 6 Expires: June 22, 2015 8 The 'Basic' HTTP Authentication Scheme 9 draft-ietf-httpauth-basicauth-update-04 11 Abstract 13 This document defines the "Basic" Hypertext Transfer Protocol (HTTP) 14 Authentication Scheme, which transmits credentials as userid/password 15 pairs, obfuscated by the use of Base64 encoding. 17 Editorial Note (To be removed by RFC Editor before publication) 19 Discussion of this draft takes place on the HTTPAuth working group 20 mailing list (http-auth@ietf.org), which is archived at . 23 XML versions, latest edits and the issues list for this document are 24 available from . 27 The changes in this draft are summarized in Appendix C.5. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on June 22, 2015. 46 Copyright Notice 48 Copyright (c) 2014 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 This document may contain material from IETF Documents or IETF 62 Contributions published or made publicly available before November 63 10, 2008. The person(s) controlling the copyright in some of this 64 material may not have granted the IETF Trust the right to allow 65 modifications of such material outside the IETF Standards Process. 66 Without obtaining an adequate license from the person(s) controlling 67 the copyright in such materials, this document may not be modified 68 outside the IETF Standards Process, and derivative works of it may 69 not be created outside the IETF Standards Process, except to format 70 it for publication as an RFC or to translate it into languages other 71 than English. 73 Table of Contents 75 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 76 1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 4 77 1.1.1. Syntax Notation . . . . . . . . . . . . . . . . . . . 4 78 2. The 'Basic' Authentication Scheme . . . . . . . . . . . . . . 4 79 2.1. The 'charset' auth-param . . . . . . . . . . . . . . . . . 6 80 2.2. Re-using Credentials . . . . . . . . . . . . . . . . . . . 8 81 3. Internationalization Considerations . . . . . . . . . . . . . 8 82 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 83 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 84 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 85 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 86 7.1. Normative References . . . . . . . . . . . . . . . . . . . 11 87 7.2. Informative References . . . . . . . . . . . . . . . . . . 11 88 Appendix A. Changes from RFC 2617 . . . . . . . . . . . . . . . . 12 89 Appendix B. Deployment Considerations for the 'charset' 90 Parameter . . . . . . . . . . . . . . . . . . . . . . 12 91 B.1. User Agents . . . . . . . . . . . . . . . . . . . . . . . 12 92 B.2. Origin Servers . . . . . . . . . . . . . . . . . . . . . . 13 93 B.3. Why not simply switch the default encoding to UTF-8? . . . 13 94 Appendix C. Change Log (to be removed by RFC Editor before 95 publication) . . . . . . . . . . . . . . . . . . . . 13 96 C.1. Since RFC 2617 . . . . . . . . . . . . . . . . . . . . . . 13 97 C.2. Since draft-ietf-httpauth-basicauth-update-00 . . . . . . 13 98 C.3. Since draft-ietf-httpauth-basicauth-update-01 . . . . . . 14 99 C.4. Since draft-ietf-httpauth-basicauth-update-02 . . . . . . 14 100 C.5. Since draft-ietf-httpauth-basicauth-update-03 . . . . . . 14 102 1. Introduction 104 This document defines the "Basic" Hypertext Transfer Protocol (HTTP) 105 Authentication Scheme, which transmits credentials as userid/password 106 pairs, obfuscated by the use of Base64 encoding (HTTP authentication 107 schemes are defined in [RFC7235]). 109 This scheme is not considered to be a secure method of user 110 authentication unless used in conjunction with some external secure 111 system such as TLS (Transport Layer Security, [RFC5246]), as the user 112 name and password are passed over the network as cleartext. 114 The "Basic" scheme previously was defined in Section 2 of [RFC2617]. 115 This document updates the definition, and also addresses 116 internationalization issues by introducing the "charset" 117 authentication parameter (Section 2.1). 119 Other documents updating RFC 2617 are "Hypertext Transfer Protocol 120 (HTTP/1.1): Authentication" ([RFC7235], defining the authentication 121 framework) and "HTTP Digest Access Authentication" ([DIGEST], 122 updating the definition of the '"Digest" authentication scheme). 123 Taken together, these three documents obsolete RFC 2617. 125 1.1. Notational Conventions 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 129 document are to be interpreted as described in [RFC2119]. 131 1.1.1. Syntax Notation 133 This specification uses the Augmented Backus-Naur Form (ABNF) 134 notation of [RFC5234]. 136 The terms protection space and realm are defined in Section 2.2 of 137 [RFC7235]. 139 The terms (character) repertoire and character encoding scheme are 140 defined in Section 2 of [RFC6365]. 142 2. The 'Basic' Authentication Scheme 144 The "Basic" authentication scheme is based on the model that the 145 client needs to authenticate itself with a user-ID and a password for 146 each protection space ("realm"). The realm value is an opaque string 147 which can only be compared for equality with other realms on that 148 server. The server will service the request only if it can validate 149 the user-ID and password for the protection space applying to the 150 requested resource. 152 The "Basic" authentication scheme utilizes the Authentication 153 Framework as follows: 155 In challenges: 157 o the scheme name is "Basic" 159 o the authentication parameter "realm" is REQUIRED ([RFC7235], 160 Section 2.2) 162 o the authentication parameter "charset" is OPTIONAL (see 163 Section 2.1) 165 o no other authentication parameters are defined -- unknown 166 parameters MUST be ignored by recipients, and new parameters can 167 only be defined by revising this specification 169 Note that both scheme and parameter names are matched case- 170 insensitively. 172 For credentials, the "token68" syntax defined in Section 2.1 of 173 [RFC7235] is used. The value is computed based on user-id and 174 password as defined below. 176 Upon receipt of a request for a URI within the protection space that 177 lacks credentials, the server can reply with a challenge using the 178 401 (Unauthorized) status code ([RFC7235], Section 3.1) and the WWW- 179 Authenticate header field ([RFC7235], Section 4.1). 181 For instance: 183 HTTP/1.1 401 Unauthorized 184 Date: Mon, 04 Feb 2014 16:50:53 GMT 185 WWW-Authenticate: Basic realm="WallyWorld" 187 ...where "WallyWorld" is the string assigned by the server to 188 identify the protection space. 190 A proxy can respond with a similar challenge using the 407 (Proxy 191 Authentication Required) status code ([RFC7235], Section 3.2) and the 192 Proxy-Authenticate header field ([RFC7235], Section 4.3). 194 To receive authorization, the client 195 1. obtains the userid and password from the user, 197 2. constructs the user-pass by concatenating userid, a single colon 198 (":") character, and the password, 200 3. encodes the user-pass into an octet sequence (see below for a 201 discussion of character encoding schemes), 203 4. and obtains the basic-credentials by encoding this octet sequence 204 using base64 ([RFC4648], Section 4) into a sequence of US-ASCII 205 characters ([RFC0020]). 207 The original definition of this authentication scheme failed to 208 specify the character encoding scheme used to convert the user-pass 209 into an octet sequence. In practice, most implementations chose 210 either a local-specific encoding such as ISO-8859-1 ([ISO-8859-1]), 211 or UTF-8 ([RFC3629]). For backwards compatibility reasons, this 212 specification continues to leave the default encoding undefined, as 213 long as it is compatible with US-ASCII (mapping any US-ASCII 214 character to a single octet matching the US-ASCII character code). 216 The userid and password MUST NOT contain any control characters (see 217 "CTL" in Appendix B.1 of [RFC5234]). 219 Furthermore, a userid containing a colon character is invalid, as 220 recipients will split the user-pass at the first occurence of a colon 221 character. Note that many user agents however will accept a colon in 222 userid, thereby producing a user-pass string that recipients will 223 likely treat in a way not intended by the user. 225 If the user agent wishes to send the userid "Aladdin" and password 226 "open sesame", it would use the following header field: 228 Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ== 230 2.1. The 'charset' auth-param 232 In challenges, servers can use the "charset" authentication parameter 233 to indicate the character encoding scheme they expect the user agent 234 to use when generating "user-pass" (a sequence of octets). This 235 information is purely advisory. 237 The only allowed value is "UTF-8", to be matched case-insensitively 238 (see [RFC2978], Section 2.3). It indicates that the server expects 239 character data to be converted to Unicode Normalization Form C 240 ("NFC", see Section 3 of [RFC5198]) and to be encoded into octets 241 using the UTF-8 character encoding scheme ([RFC3629]). 243 For the userid, recipients MUST support all characters defined in the 244 "UsernameCasePreserved" profile defined in in Section 3.3 of 245 [PRECIS], with the exception of the colon (":") character. 247 For the password, recipients MUST support all characters defined in 248 the "OpaqueString" profile defined in in Section 4.2 of [PRECIS]. 250 Other values are reserved for future use. 252 Note: The 'charset' is only defined on challenges, as "Basic" uses 253 a single token for credentials ('token68' syntax), thus the 254 credentials syntax isn't extensible. 256 Note: The name 'charset' has been chosen for consistency with 257 Section 2.1.1 of [RFC2831]. A better name would have been 258 'accept-charset', as it is not about the message it appears in, 259 but the server's expectation. 261 In the example below, the server prompts for authentication in the 262 "foo" realm, using Basic authentication, with a preference for the 263 UTF-8 character encoding scheme: 265 WWW-Authenticate: Basic realm="foo", charset="UTF-8" 267 Note that the parameter value can be either a token or a quoted 268 string; in this case the server chose to use the quoted-string 269 notation. 271 The user's name is "test", and the password is the string "123" 272 followed by the Unicode character U+00A3 (POUND SIGN). Using the 273 character encoding scheme UTF-8, the user-pass becomes: 275 't' 'e' 's' 't' ':' '1' '2' '3' pound 276 74 65 73 74 3A 31 32 33 C2 A3 278 Encoding this octet sequence in Base64 ([RFC4648], Section 4) yields: 280 dGVzdDoxMjPCow== 282 Thus the Authorization header field would be: 284 Authorization: Basic dGVzdDoxMjPCow== 286 Or, for proxy authentication: 288 Proxy-Authorization: Basic dGVzdDoxMjPCow== 290 2.2. Re-using Credentials 292 Given the absolute URI ([RFC3986], Section 4.3) of an authenticated 293 request, the authentication scope of that request is obtained by 294 removing all characters after the last slash ("/") character. A 295 client SHOULD assume that resources identified by URIs with a prefix- 296 match of the authentication scope are also within the protection 297 space specified by the realm value of the that authenticated request. 299 A client MAY preemptively send the corresponding Authorization header 300 field with requests for resources in that space without receipt of 301 another challenge from the server. Similarly, when a client sends a 302 request to a proxy, it may reuse a userid and password in the Proxy- 303 Authorization header field without receiving another challenge from 304 the proxy server. 306 For example, given an authenticated request to: 308 http://example.com/docs/index.html 310 ...requests to the URIs below could use the known credentials: 312 http://example.com/docs/ 313 http://example.com/docs/test.doc 314 http://example.com/docs/?page=1 316 ...while the URIs 318 http://example.com/other/ 319 https://example.com/docs/ 321 would be considered to be outside the authentication scope. 323 Note that a URI can be part of multiple authentication scopes (such 324 as "http://example.com/" and "http://example.com/docs/"). This 325 specification does not define which of these should be treated with 326 higher priority. 328 3. Internationalization Considerations 330 User names or passwords containing characters outside the US-ASCII 331 character repertoire will cause interoperability issues, unless both 332 communication partners agree on what character encoding scheme is to 333 be used. Servers can use the new 'charset' parameter (Section 2.1) 334 to indicate a preference of "UTF-8", increasing the probability that 335 clients will switch to that encoding. 337 The "realm" parameter carries data that can be considered textual, 338 however [RFC7235] does not define a way to reliably transport non-US- 339 ASCII characters. This is a known issue that would need to be 340 addressed in that specification. 342 4. Security Considerations 344 The Basic authentication scheme is not a secure method of user 345 authentication, nor does it in any way protect the entity, which is 346 transmitted in cleartext across the physical network used as the 347 carrier. HTTP does not prevent the addition of enhancements (such as 348 schemes to use one-time passwords) to Basic authentication. 350 The most serious flaw in Basic authentication is that it results in 351 the cleartext transmission of the user's password over the physical 352 network. Many other authentication schemes address this problem. 354 Because Basic authentication involves the cleartext transmission of 355 passwords it SHOULD NOT be used (without enhancements such as HTTPS 356 [RFC2818]) to protect sensitive or valuable information. 358 A common use of Basic authentication is for identification purposes 359 -- requiring the user to provide a user name and password as a means 360 of identification, for example, for purposes of gathering accurate 361 usage statistics on a server. When used in this way it is tempting 362 to think that there is no danger in its use if illicit access to the 363 protected documents is not a major concern. This is only correct if 364 the server issues both user name and password to the users and in 365 particular does not allow the user to choose his or her own password. 366 The danger arises because naive users frequently reuse a single 367 password to avoid the task of maintaining multiple passwords. 369 If a server permits users to select their own passwords, then the 370 threat is not only unauthorized access to documents on the server but 371 also unauthorized access to any other resources on other systems that 372 the user protects with the same password. Furthermore, in the 373 server's password database, many of the passwords may also be users' 374 passwords for other sites. The owner or administrator of such a 375 system could therefore expose all users of the system to the risk of 376 unauthorized access to all those sites if this information is not 377 maintained in a secure fashion. This raises both security and 378 privacy concerns ([RFC6973]). If the same username and password 379 combination is in use to access other accounts, such as an email or 380 health portal account, personal information could be exposed. 382 Basic Authentication is also vulnerable to spoofing by counterfeit 383 servers. If a user can be led to believe that he is connecting to a 384 host containing information protected by Basic authentication when, 385 in fact, he is connecting to a hostile server or gateway, then the 386 attacker can request a password, store it for later use, and feign an 387 error. This type of attack is not possible with Digest 388 Authentication. Server implementers SHOULD guard against the 389 possibility of this sort of counterfeiting by gateways or CGI 390 scripts. In particular it is very dangerous for a server to simply 391 turn over a connection to a gateway. That gateway can then use the 392 persistent connection mechanism to engage in multiple transactions 393 with the client while impersonating the original server in a way that 394 is not detectable by the client. 396 The use of the UTF-8 character encoding scheme introduces additional 397 security considerations; see Section 10 of [RFC3629] for more 398 information. 400 5. IANA Considerations 402 IANA maintains the registry of HTTP Authentication Schemes 403 ([RFC7235]) at . 405 The entry for the "Basic" Authentication Scheme shall be updated with 406 a pointer to this specification. 408 6. Acknowledgements 410 This specification takes over the definition of the "Basic" HTTP 411 Authentication Scheme, previously defined in RFC 2617. We thank John 412 Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D. 413 Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for 414 their work on that specification, from which significant amounts of 415 text were borrowed. See Section 6 of [RFC2617] for further 416 acknowledgements. 418 The internationalization problem with respect to the character 419 encoding scheme used for user-pass has been reported as a Mozilla bug 420 back in the year 2000 (see 421 and also the 422 more recent ). 423 It was Andrew Clover's idea to address it using a new auth-param. 425 We also thank the members of the HTTPAuth Working Group and other 426 reviewers, namely Stephen Farrell, Bjoern Hoehrmann, Kari Hurtta, 427 Amos Jeffries, Benjamin Kaduk, James Manger, Kathleen Moriarty, Yaron 428 Sheffer, Michael Sweet, and Martin Thomson for feedback on this 429 revision. 431 7. References 432 7.1. Normative References 434 [PRECIS] Saint-Andre, P. and A. Melnikov, "Preparation, 435 Enforcement, and Comparison of Internationalized 436 Strings Representing Usernames and Passwords", 437 draft-ietf-precis-saslprepbis-12 (work in progress), 438 December 2014. 440 [RFC0020] Cerf, V., "ASCII format for network interchange", 441 RFC 20, October 1969. 443 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 444 Requirement Levels", BCP 14, RFC 2119, March 1997. 446 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration 447 Procedures", BCP 19, RFC 2978, October 2000. 449 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 450 10646", STD 63, RFC 3629, November 2003. 452 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, 453 "Uniform Resource Identifier (URI): Generic Syntax", 454 STD 66, RFC 3986, January 2005. 456 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 457 Encodings", RFC 4648, October 2006. 459 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for 460 Network Interchange", RFC 5198, March 2008. 462 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for 463 Syntax Specifications: ABNF", STD 68, RFC 5234, 464 January 2008. 466 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 467 Internationalization in the IETF", BCP 166, RFC 6365, 468 September 2011. 470 [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext 471 Transfer Protocol (HTTP/1.1): Authentication", 472 RFC 7235, June 2014. 474 7.2. Informative References 476 [DIGEST] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP 477 Digest Access Authentication", 478 draft-ietf-httpauth-digest-09 (work in progress), 479 December 2014. 481 [ISO-8859-1] International Organization for Standardization, 482 "Information technology -- 8-bit single-byte coded 483 graphic character sets -- Part 1: Latin alphabet No. 484 1", ISO/IEC 8859-1:1998, 1998. 486 [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, 487 S., Leach, P., Luotonen, A., and L. Stewart, "HTTP 488 Authentication: Basic and Digest Access 489 Authentication", RFC 2617, June 1999. 491 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 493 [RFC2831] Leach, P. and C. Newman, "Using Digest Authentication 494 as a SASL Mechanism", RFC 2831, May 2000. 496 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer 497 Security (TLS) Protocol Version 1.2", RFC 5246, 498 August 2008. 500 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 501 Morris, J., Hansen, M., and R. Smith, "Privacy 502 Considerations for Internet Protocols", RFC 6973, 503 July 2013. 505 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext 506 Transfer Protocol (HTTP/1.1): Semantics and Content", 507 RFC 7231, June 2014. 509 Appendix A. Changes from RFC 2617 511 The scheme definition has been rewritten to be consistent with newer 512 specifications such as [RFC7235]. 514 The new authentication parameter "charset" has been added. It is 515 purely advisory, so existing implementations do not need to change, 516 unless they want to take advantage of the additional information 517 which previously wasn't available. 519 Appendix B. Deployment Considerations for the 'charset' Parameter 521 B.1. User Agents 523 User agents not implementing 'charset' will continue to work as 524 before, ignoring the new parameter. 526 User agents which already default to the UTF-8 encoding implement 527 'charset' by definition. 529 Other user agents can keep their default behavior, and switch to 530 UTF-8 when seeing the new parameter. 532 B.2. Origin Servers 534 Origin servers that do not support non-US-ASCII characters in 535 credentials do not require any changes to support 'charset'. 537 Origin servers that need to support non-US-ASCII characters, but 538 cannot use the UTF-8 character encoding scheme will not be affected; 539 they will continue to function as well or as badly as before. 541 Finally, origin servers that need to support non-US-ASCII characters 542 and can use the UTF-8 character encoding scheme can opt in as 543 described above. In the worst case, they'll continue to see either 544 broken credentials or no credentials at all (depending on how legacy 545 clients handle characters they can not encode). 547 B.3. Why not simply switch the default encoding to UTF-8? 549 There are sites in use today that default to a local character 550 encoding scheme, such as ISO-8859-1 ([ISO-8859-1]), and expect user 551 agents to use that encoding. Authentication on these sites will stop 552 to work if the user agent switches to a different encoding, such as 553 UTF-8. 555 Note that sites might even inspect the User-Agent header field 556 ([RFC7231], Section 5.5.3) to decide what character encoding scheme 557 to expect from the client. Therefore they might support UTF-8 for 558 some user agents, but default to something else for others. User 559 agents in the latter group will have to continue to do what they do 560 today until the majority of these servers have been upgraded to 561 always use UTF-8. 563 Appendix C. Change Log (to be removed by RFC Editor before publication) 565 C.1. Since RFC 2617 567 This draft acts as a baseline for tracking subsequent changes to the 568 specification. As such, it extracts the definition of "Basic", plus 569 the related Security Considerations, and also adds the IANA 570 registration of the scheme. Changes to the actual definition will be 571 made in subsequent drafts. 573 C.2. Since draft-ietf-httpauth-basicauth-update-00 575 Fixed Base64 reference to point to an actual definition of Base64. 577 Update HTTPbis and Digest references. 579 Note that this spec, together with HTTPbis P7 and the Digest update, 580 obsoletes RFC 2617. 582 Rewrote text about authentication parameters and their extensibility. 584 Pulled in the definition of the "charset" parameter. 586 Removed a misleading statement about userids potentially being case- 587 sensitive, as the same is true for passwords. 589 Added TODOs with respect to path matching, and colons in userids. 591 C.3. Since draft-ietf-httpauth-basicauth-update-01 593 Minor improvements on Security Considerations. 595 Update Digest reference. 597 Rewrite scheme definition as algorithm rather than pseudo-ABNF. 599 Add a note about colons in userid. 601 Attempt to explain authentication scopes. 603 C.4. Since draft-ietf-httpauth-basicauth-update-02 605 Reference draft-ietf-precis-saslprepbis for the set of characters 606 that need to be supported in userids and passwords. 608 C.5. Since draft-ietf-httpauth-basicauth-update-03 610 Update reference for draft-ietf-precis-saslprepbis (which renames 611 "Password" to "OpaqueString"). 613 Mention HTTPS as enhancement for securing the transmission of 614 credentials. 616 Update DIGEST reference and change it to informative. 618 Use RFC 20 as reference for ASCII. 620 Author's Address 622 Julian F. Reschke 623 greenbytes GmbH 624 Hafenweg 16 625 Muenster, NW 48155 626 Germany 628 EMail: julian.reschke@greenbytes.de 629 URI: http://greenbytes.de/tech/webdav/