Difference between revisions of "RFC4959"
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Initial Client Response | Initial Client Response | ||
− | Status of This Memo | + | '''Status of This Memo''' |
This document specifies an Internet standards track protocol for the | This document specifies an Internet standards track protocol for the | ||
Internet community, and requests discussion and suggestions for | Internet community, and requests discussion and suggestions for | ||
improvements. Please refer to the current edition of the "Internet | improvements. Please refer to the current edition of the "Internet | ||
− | Official Protocol Standards" (STD 1) for the standardization state | + | Official Protocol Standards" ([[STD1|STD 1]]) for the standardization state |
and status of this protocol. Distribution of this memo is unlimited. | and status of this protocol. Distribution of this memo is unlimited. | ||
− | Abstract | + | '''Abstract''' |
To date, the Internet Message Access Protocol (IMAP) has used a | To date, the Internet Message Access Protocol (IMAP) has used a | ||
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The SASL initial client response extension is present in any IMAP | The SASL initial client response extension is present in any IMAP | ||
− | [RFC3501] server implementation which returns "SASL-IR" as one of the | + | [[RFC3501]] server implementation which returns "SASL-IR" as one of the |
supported capabilities in its CAPABILITY response. | supported capabilities in its CAPABILITY response. | ||
Servers which support this extension will accept an optional initial | Servers which support this extension will accept an optional initial | ||
− | client response with the AUTHENTICATE command for any SASL [RFC4422] | + | client response with the AUTHENTICATE command for any SASL [[RFC4422]] |
mechanisms which support it. | mechanisms which support it. | ||
Line 43: | Line 43: | ||
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | ||
− | document are to be interpreted as described in [RFC2119]. | + | document are to be interpreted as described in [[RFC2119]]. |
In examples, "C:" and "S:" indicate lines sent by the client and | In examples, "C:" and "S:" indicate lines sent by the client and | ||
server, respectively. | server, respectively. | ||
− | Formal syntax is defined by [RFC4234] as extended by [RFC3501]. | + | Formal syntax is defined by [[RFC4234]] as extended by [[RFC3501]]. |
== IMAP Changes to the IMAP AUTHENTICATE Command == | == IMAP Changes to the IMAP AUTHENTICATE Command == | ||
This extension adds an optional second argument to the AUTHENTICATE | This extension adds an optional second argument to the AUTHENTICATE | ||
− | command that is defined in Section 6.2.2 of [RFC3501]. If this | + | command that is defined in Section 6.2.2 of [[RFC3501]]. If this |
second argument is present, it represents the contents of the | second argument is present, it represents the contents of the | ||
− | "initial client response" defined in Section 5.1 of [RFC4422]. | + | "initial client response" defined in Section 5.1 of [[RFC4422]]. |
As with any other client response, this initial client response MUST | As with any other client response, this initial client response MUST | ||
− | be encoded as defined in Section 4 of [RFC4648]. It also MUST be | + | be encoded as defined in Section 4 of [[RFC4648]]. It also MUST be |
transmitted outside of a quoted string or literal. To send a zero- | transmitted outside of a quoted string or literal. To send a zero- | ||
length initial response, the client MUST send a single pad character | length initial response, the client MUST send a single pad character | ||
Line 64: | Line 64: | ||
length string. | length string. | ||
− | When decoding the BASE64 [RFC4648] data in the initial client | + | When decoding the BASE64 [[RFC4648]] data in the initial client |
− | response, decoding errors MUST be treated as IMAP [RFC3501] would | + | response, decoding errors MUST be treated as IMAP [[RFC3501]] would |
handle them in any normal SASL client response. In particular, the | handle them in any normal SASL client response. In particular, the | ||
server should check for any characters not explicitly allowed by the | server should check for any characters not explicitly allowed by the | ||
Line 81: | Line 81: | ||
that implement this extension MUST NOT send an initial client | that implement this extension MUST NOT send an initial client | ||
response to servers that do not advertise the SASL-IR capability. In | response to servers that do not advertise the SASL-IR capability. In | ||
− | such a situation, clients MUST fall back to an IMAP [RFC3501] | + | such a situation, clients MUST fall back to an IMAP [[RFC3501]] |
compatible mode. | compatible mode. | ||
Line 87: | Line 87: | ||
capability, a mechanism which uses an initial client response is | capability, a mechanism which uses an initial client response is | ||
negotiated using the challenge/response exchange described in | negotiated using the challenge/response exchange described in | ||
− | [RFC3501], with an initial zero-length server challenge. | + | [[RFC3501]], with an initial zero-length server challenge. |
== Examples == | == Examples == | ||
The following is an example authentication using the PLAIN (see | The following is an example authentication using the PLAIN (see | ||
− | [RFC4616]) SASL mechanism (under a TLS protection layer, see | + | [[RFC4616]]) SASL mechanism (under a TLS protection layer, see |
− | [RFC4346]) and an initial client response: | + | [[RFC4346]]) and an initial client response: |
... client connects to server and negotiates a TLS | ... client connects to server and negotiates a TLS | ||
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The following is an example authentication using the SASL EXTERNAL | The following is an example authentication using the SASL EXTERNAL | ||
− | mechanism (defined in [RFC4422]) under a TLS protection layer (see | + | mechanism (defined in [[RFC4422]]) under a TLS protection layer (see |
− | [RFC4346]) and an empty initial client response: | + | [[RFC4346]]) and an empty initial client response: |
... client connects to server and negotiates a TLS | ... client connects to server and negotiates a TLS | ||
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The extension defined in this document is subject to many of the | The extension defined in this document is subject to many of the | ||
− | Security Considerations defined in [RFC3501] and [RFC4422]. | + | Security Considerations defined in [[RFC3501]] and [[RFC4422]]. |
Server implementations MUST treat the omission of an initial client | Server implementations MUST treat the omission of an initial client | ||
− | response from the AUTHENTICATE command as defined by [RFC3501] (as if | + | response from the AUTHENTICATE command as defined by [[RFC3501]] (as if |
this extension did not exist). | this extension did not exist). | ||
− | Although [RFC3501] has no express line length limitations, some | + | Although [[RFC3501]] has no express line length limitations, some |
implementations choose to enforce them anyway. Such implementations | implementations choose to enforce them anyway. Such implementations | ||
MUST be aware that the addition of the initial response parameter to | MUST be aware that the addition of the initial response parameter to | ||
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The following syntax specification uses the Augmented Backus-Naur | The following syntax specification uses the Augmented Backus-Naur | ||
− | Form [RFC4234] notation. [RFC3501] defines the non-terminals | + | Form [[RFC4234]] notation. [[RFC3501]] defines the non-terminals |
capability, auth-type, and base64. | capability, auth-type, and base64. | ||
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authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")] | authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")] | ||
*(CRLF base64) | *(CRLF base64) | ||
− | ;;redefine AUTHENTICATE from [RFC3501] | + | ;;redefine AUTHENTICATE from [[RFC3501]] |
== Acknowledgments == | == Acknowledgments == | ||
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=== Normative References === | === Normative References === | ||
− | [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate | + | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate |
− | Requirement Levels", BCP 14, RFC 2119, March 1997. | + | Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]], March 1997. |
− | [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION | + | [[RFC3501]] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION |
− | 4rev1", RFC 3501, March 2003. | + | 4rev1", [[RFC3501|RFC 3501]], March 2003. |
− | [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax | + | [[RFC4234]] Crocker, D. and P. Overell, "Augmented BNF for Syntax |
− | Specifications: ABNF", RFC 4234, October 2005. | + | Specifications: ABNF", [[RFC4234|RFC 4234]], October 2005. |
− | [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and | + | [[RFC4422]] Melnikov, A. and K. Zeilenga, "Simple Authentication and |
− | Security Layer (SASL)", RFC 4422, June 2006. | + | Security Layer (SASL)", [[RFC4422|RFC 4422]], June 2006. |
− | [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data | + | [[RFC4648]] Josefsson, S., "The Base16, Base32, and Base64 Data |
− | Encodings", RFC 4648, October 2006. | + | Encodings", [[RFC4648|RFC 4648]], October 2006. |
=== Informative References === | === Informative References === | ||
− | [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and | + | [[RFC4616]] Zeilenga, K., "The PLAIN Simple Authentication and |
− | Security Layer (SASL) Mechanism", RFC 4616, August 2006. | + | Security Layer (SASL) Mechanism", [[RFC4616|RFC 4616]], August 2006. |
− | [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security | + | [[RFC4346]] Dierks, T. and E. Rescorla, "The Transport Layer Security |
− | (TLS) Protocol Version 1.1", RFC 4346, April 2006. | + | (TLS) Protocol Version 1.1", [[RFC4346|RFC 4346]], April 2006. |
Authors' Addresses | Authors' Addresses | ||
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This document is subject to the rights, licenses and restrictions | This document is subject to the rights, licenses and restrictions | ||
− | contained in BCP 78, and except as set forth therein, the authors | + | contained in [[BCP78|BCP 78]], and except as set forth therein, the authors |
retain all their rights. | retain all their rights. | ||
Line 258: | Line 258: | ||
made any independent effort to identify any such rights. Information | made any independent effort to identify any such rights. Information | ||
on the procedures with respect to rights in RFC documents can be | on the procedures with respect to rights in RFC documents can be | ||
− | found in BCP 78 and BCP 79. | + | found in [[BCP78|BCP 78]] and [[BCP79|BCP 79]]. |
Copies of IPR disclosures made to the IETF Secretariat and any | Copies of IPR disclosures made to the IETF Secretariat and any | ||
Line 272: | Line 272: | ||
this standard. Please address the information to the IETF at | this standard. Please address the information to the IETF at | ||
+ | |||
+ | [[Category:Standards Track]] |
Latest revision as of 20:03, 5 October 2020
Network Working Group R. Siemborski Request for Comments: 4959 Google, Inc. Category: Standards Track A. Gulbrandsen
Oryx Mail Systems GmbH September 2007
IMAP Extension for Simple Authentication and Security Layer (SASL)
Initial Client Response
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Abstract
To date, the Internet Message Access Protocol (IMAP) has used a Simple Authentication and Security Layer (SASL) profile which always required at least one complete round trip for an authentication, as it did not support an initial client response argument. This additional round trip at the beginning of the session is undesirable, especially when round-trip costs are high.
This document defines an extension to IMAP which allows clients and servers to avoid this round trip by allowing an initial client response argument to the IMAP AUTHENTICATE command.
Contents
Introduction
The SASL initial client response extension is present in any IMAP RFC3501 server implementation which returns "SASL-IR" as one of the supported capabilities in its CAPABILITY response.
Servers which support this extension will accept an optional initial client response with the AUTHENTICATE command for any SASL RFC4422 mechanisms which support it.
Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.
In examples, "C:" and "S:" indicate lines sent by the client and server, respectively.
Formal syntax is defined by RFC4234 as extended by RFC3501.
IMAP Changes to the IMAP AUTHENTICATE Command
This extension adds an optional second argument to the AUTHENTICATE command that is defined in Section 6.2.2 of RFC3501. If this second argument is present, it represents the contents of the "initial client response" defined in Section 5.1 of RFC4422.
As with any other client response, this initial client response MUST be encoded as defined in Section 4 of RFC4648. It also MUST be transmitted outside of a quoted string or literal. To send a zero- length initial response, the client MUST send a single pad character ("="). This indicates that the response is present, but is a zero- length string.
When decoding the BASE64 RFC4648 data in the initial client response, decoding errors MUST be treated as IMAP RFC3501 would handle them in any normal SASL client response. In particular, the server should check for any characters not explicitly allowed by the BASE64 alphabet, as well as any sequence of BASE64 characters that contains the pad character ('=') anywhere other than the end of the string (e.g., "=AAA" and "AAA=BBB" are not allowed).
If the client uses an initial response with a SASL mechanism that does not support an initial response, the server MUST reject the command with a tagged BAD response.
Note: support and use of the initial client response is optional for both clients and servers. Servers that implement this extension MUST support clients that omit the initial client response, and clients that implement this extension MUST NOT send an initial client response to servers that do not advertise the SASL-IR capability. In such a situation, clients MUST fall back to an IMAP RFC3501 compatible mode.
If either the client or the server do not support the SASL-IR capability, a mechanism which uses an initial client response is negotiated using the challenge/response exchange described in RFC3501, with an initial zero-length server challenge.
Examples
The following is an example authentication using the PLAIN (see RFC4616) SASL mechanism (under a TLS protection layer, see RFC4346) and an initial client response:
... client connects to server and negotiates a TLS protection layer ... C: C01 CAPABILITY S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN S: C01 OK Completed C: A01 AUTHENTICATE PLAIN dGVzdAB0ZXN0AHRlc3Q= S: A01 OK Success (tls protection)
Note that even when a server supports this extension, the following negotiation (which does not use the initial response) is still valid and MUST be supported by the server:
... client connects to server and negotiates a TLS protection layer ... C: C01 CAPABILITY S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN S: C01 OK Completed C: A01 AUTHENTICATE PLAIN (note that there is a space following the "+" in the following line) S: + C: dGVzdAB0ZXN0AHRlc3Q= S: A01 OK Success (tls protection)
The following is an example authentication using the SASL EXTERNAL mechanism (defined in RFC4422) under a TLS protection layer (see RFC4346) and an empty initial client response:
... client connects to server and negotiates a TLS protection layer ... C: C01 CAPABILITY S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL S: C01 OK Completed C: A01 AUTHENTICATE EXTERNAL = S: A01 OK Success (tls protection)
This is in contrast with the handling of such a situation when an initial response is omitted:
... client connects to server and negotiates a TLS protection layer ... C: C01 CAPABILITY S: * CAPABILITY IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL S: C01 OK Completed C: A01 AUTHENTICATE EXTERNAL (note that there is a space following the "+" in the following line) S: + C: S: A01 OK Success (tls protection)
IANA Considerations
The IANA has added SASL-IR to the IMAP4 Capabilities Registry.
Security Considerations
The extension defined in this document is subject to many of the Security Considerations defined in RFC3501 and RFC4422.
Server implementations MUST treat the omission of an initial client response from the AUTHENTICATE command as defined by RFC3501 (as if this extension did not exist).
Although RFC3501 has no express line length limitations, some implementations choose to enforce them anyway. Such implementations MUST be aware that the addition of the initial response parameter to AUTHENTICATE may increase the maximum line length that IMAP parsers may expect to support. Server implementations MUST be able to receive the largest possible initial client response that their supported mechanisms might receive.
Formal Syntax
The following syntax specification uses the Augmented Backus-Naur Form RFC4234 notation. RFC3501 defines the non-terminals capability, auth-type, and base64.
capability =/ "SASL-IR"
authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")] *(CRLF base64) ;;redefine AUTHENTICATE from RFC3501
Acknowledgments
The authors would like to acknowledge the contributions of Ken Murchison and Mark Crispin, along with the rest of the IMAPEXT Working Group for their assistance in reviewing this document.
Alexey Melnikov and Cyrus Daboo also had some early discussions about this extension.
References
Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC3501 Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
RFC4234 Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
RFC4422 Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
RFC4648 Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
Informative References
RFC4616 Zeilenga, K., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, August 2006.
RFC4346 Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
Authors' Addresses
Robert Siemborski Google, Inc. 1600 Ampitheatre Parkway Mountain View, CA 94043
Phone: +1 650 623 6925 EMail: [email protected]
Arnt Gulbrandsen Oryx Mail Systems GmbH Schweppermannstr. 8 D-81671 Muenchen Germany
EMail: [email protected]
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at [email protected].