bincimap

rfc2221.txt (9251B)

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 Network Working Group                                           M. Gahrns
 Request for Comments: 2221                                      Microsoft
 Category: Standards Track                                    October 1997
 
 
                          IMAP4 Login Referrals
 
 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.
 
 Copyright Notice
 
    Copyright (C) The Internet Society (1997).  All Rights Reserved.
 
 1. Abstract
 
    When dealing with large amounts of users and many IMAP4 [RFC-2060]
    servers, it is often necessary to move users from one IMAP4 server to
    another.  For example, hardware failures or organizational changes
    may dictate such a move.
 
    Login referrals allow clients to transparently connect to an
    alternate IMAP4 server, if their home IMAP4 server has changed.
 
    A referral mechanism can provide efficiencies over the alternative
    'proxy method', in which the local IMAP4 server contacts the remote
    server on behalf of the client, and then transfers the data from the
    remote server to itself, and then on to the client.  The referral
    mechanism's direct client connection to the remote server is often a
    more efficient use of bandwidth, and does not require the local
    server to impersonate the client when authenticating to the remote
    server.
 
 2. Conventions used in this document
 
    In examples, "C:" and "S:" indicate lines sent by the client and
    server respectively.
 
    A home server, is an IMAP4 server that contains the user's inbox.
 
    A remote server is a server that contains remote mailboxes.
 
 
 
 
 
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 RFC 2221                 IMAP4 Login Referrals              October 1997
 
 
    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 [RFC-2119].
 
 3. Introduction and Overview
 
    IMAP4 servers that support this extension MUST list the keyword
    LOGIN-REFERRALS in their CAPABILITY response.  No client action is
    needed to invoke the LOGIN-REFERRALS capability in a server.
 
    A LOGIN-REFERRALS capable IMAP4 server SHOULD NOT return a referral
    to a server that will return a referral. A client MUST NOT follow
    more than 10 levels of referral without consulting the user.
 
    A LOGIN-REFERRALS response code MUST contain as an argument a valid
    IMAP server URL as defined in [IMAP-URL].
 
    A home server referral consists of either a tagged NO or OK, or an
    untagged BYE response that contains a LOGIN-REFERRALS response code.
 
    Example: A001 NO [REFERRAL IMAP://user;AUTH=*@SERVER2/] Remote Server
 
    NOTE: user;AUTH=* is specified as required by [IMAP-URL] to avoid a
    client falling back to anonymous login.
 
 4. Home Server Referrals
 
    A home server referral may be returned in response to an AUTHENTICATE
    or LOGIN command, or it may appear in the connection startup banner.
    If a server returns a home server referral in a tagged NO response,
    that server does not contain any mailboxes that are accessible to the
    user.  If a server returns a home server referral in a tagged OK
    response, it indicates that the user's personal mailboxes are
    elsewhere, but the server contains public mailboxes which are
    readable by the user.  After receiving a home server referral, the
    client can not make any assumptions as to whether this was a
    permanent or temporary move of the user.
 
 4.1.  LOGIN and AUTHENTICATE Referrals
 
    An IMAP4 server MAY respond to a LOGIN or AUTHENTICATE command with a
    home server referral if it wishes to direct the user to another IMAP4
    server.
 
    Example:  C: A001 LOGIN MIKE PASSWORD
              S: A001 NO [REFERRAL IMAP://MIKE@SERVER2/] Specified user
                      is invalid on this server. Try SERVER2.
 
 
 
 
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    Example:  C: A001 LOGIN MATTHEW PASSWORD
              S: A001 OK [REFERRAL IMAP://MATTHEW@SERVER2/] Specified
                      user's personal mailboxes located on Server2, but
                      public mailboxes are available.
 
    Example:  C: A001 AUTHENTICATE GSSAPI
              <authentication exchange>
              S: A001 NO [REFERRAL IMAP://user;AUTH=GSSAPI@SERVER2/]
                      Specified user is invalid on this server. Try
                      SERVER2.
 
 4.2. BYE at connection startup referral
 
    An IMAP4 server MAY respond with an untagged BYE and a REFERRAL
    response code that contains an IMAP URL to a home server if it is not
    willing to accept connections and wishes to direct the client to
    another IMAP4 server.
 
    Example:  S: * BYE [REFERRAL IMAP://user;AUTH=*@SERVER2/] Server not
                   accepting connections.  Try SERVER2
 
 5. Formal Syntax
 
    The following syntax specification uses the augmented Backus-Naur
    Form (BNF) as described in [ABNF].
 
    This amends the "resp_text_code" element of the IMAP4 grammar
    described in [RFC-2060]
 
    resp_text_code =/ "REFERRAL" SPACE <imapurl>
       ; See [IMAP-URL] for definition of <imapurl>
       ; See [RFC-2060] for base definition of resp_text_code
 
 6. Security Considerations
 
    The IMAP4 login referral mechanism makes use of IMAP URLs, and as
    such, have the same security considerations as general internet URLs
    [RFC-1738], and in particular IMAP URLs [IMAP-URL].
 
    A server MUST NOT give a login referral if authentication for that
    user fails. This is to avoid revealing information about the user's
    account to an unauthorized user.
 
    With the LOGIN-REFERRALS capability, it is potentially easier to
    write a rogue 'password catching' server that collects login data and
    then refers the client to their actual IMAP4 server.  Although
    referrals reduce the effort to write such a server, the referral
    response makes detection of the intrusion easier.
 
 
 
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 7. References
 
    [RFC-2060], Crispin, M., "Internet Message Access Protocol - Version
    4rev1", RFC 2060, December 1996.
 
    [IMAP-URL], Newman, C., "IMAP URL Scheme", RFC 2192, Innosoft,
    September 1997.
 
    [RFC-1738], Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
    Resource Locators  (URL)", RFC 1738, December 1994.
 
    [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate
    Requirement Levels", RFC 2119, March 1997.
 
    [ABNF], DRUMS working group, Dave Crocker Editor, "Augmented BNF for
    Syntax Specifications: ABNF", Work in Progress.
 
 8.  Acknowledgments
 
    Many valuable suggestions were received from private discussions and
    the IMAP4 mailing list.  In particular, Raymond Cheng, Mark Crispin,
    Mark Keasling Chris Newman and Larry Osterman made significant
    contributions to this document.
 
 9. Author's Address
 
    Mike Gahrns
    Microsoft
    One Microsoft Way
    Redmond, WA, 98072
 
    Phone: (206) 936-9833
    EMail: mikega@microsoft.com
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 10.  Full Copyright Statement
 
    Copyright (C) The Internet Society (1997).  All Rights Reserved.
 
    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implmentation may be prepared, copied, published
    andand distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph are
    included on all such copies and derivative works.  However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of
    developing Internet standards in which case the procedures for
    copyrights defined in the Internet Standards process must be
    followed, or as required to translate it into languages other than
    English.
 
    The limited permissions granted above are perpetual and will not be
    revoked by the Internet Society or its successors or assigns.
 
    This document and the information contained herein is provided on an
    "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
    TASK FORCE DISCLAIMS 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."
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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