Internet Draft: POP URL Scheme R. Gellens Document: draft-gellens-pop-url-01.txt QUALCOMM, Incorporated Expires: 12 August 1998 12 February 1998 POP URL Scheme Status of this Memo: This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." To learn the current status of any Internet Draft, please check the "1id-abstracts.txt" listing contained in the Internet Drafts shadow directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). A version of this draft document is intended for submission to the RFC editor as a Proposed Standard for the Internet Community. Discussion and suggestions for improvement are requested. 1. Introduction [POP3] is a widely-deployed mail access protocol. Many programs access POP3 message stores, and thus need POP3 configuration information. Since there are multiple configuration elements which are required in order to access a mailbox, a single string representation is convenient. A POP3 mailbox (like an [IMAP4] mailbox) is a network resource, and URLs are a widely-supported generalized representation of network resources. A means of specifying a POP3 mailbox as a URL will likely be useful in many programs and protocols. [ACAP] is one case where a string encapsulation of elements required to access network services is needed. For example, an [IMAP4] message store is usually specified in ACAP datasets as an [IMAP-URL]. Gellens Expires August 1998 [Page 1]
Internet Draft POP URL Scheme February 1998 This memo defines a URL scheme for referencing a POP mailbox. 2. Conventions Used in this Document The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as defined in "Key words for use in RFCs to Indicate Requirement Levels" [KEYWORDS]. 3. POP Scheme The POP URL scheme designates a POP server, and optionally a port number, authentication mechanism, authentication ID, and/or authorization ID. The POP URL follows the common Internet scheme syntax as defined in RFC 1738 [BASIC-URL] except that clear text passwords are not permitted. If :<port> is omitted, the port defaults to 110. The POP URL is described using [ABNF] in Section 8. A POP URL is of the general form: pop://<user>;auth=<auth>@<host>:<port> Where <user>, <host>, and <port> are as defined in RFC 1738, and some or all of the elements, except "pop:" and <host>, may be omitted. 4. POP User Name and Authentication Mechanism An authorization (which mailbox to access) and authentication (whose password to check against) identity (referred to as "user name" for simplicity) and/or authentication mechanism name may be supplied. These are used in the "USER", "APOP", or "AUTH" [POP-AUTH] commands after making the connection to the POP server. If the URL doesn't supply an authentication identifier, the program interpreting the POP URL SHOULD request one from the user. An authentication mechanism can be expressed by adding ";AUTH=<enc_auth_type>" to the end of the user name. If the authentication mechanism is not "APOP", it is a SASL POP [POP-AUTH] mechanism. When such an <enc_auth_type> is indicated, the client SHOULD request appropriate credentials from that mechanism and use the "AUTH" or "APOP" commands instead of the "USER" command. If no user name is specified, one SHOULD be obtained from the mechanism or requested from the user as appropriate. Gellens Expires August 1998 [Page 2]
Internet Draft POP URL Scheme February 1998 The string ";AUTH=*" indicates that the client SHOULD select an appropriate authentication mechanism. It MAY use any mechanism supported by the POP server. If a user name is included with no authentication mechanism, then ";AUTH=*" is assumed. Since URLs can easily come from untrusted sources, care must be taken when resolving a URL which requires or requests any sort of authentication. If authentication credentials are supplied to the wrong server, it may compromise the security of the user's account. The program resolving the URL should make sure it meets at least one of the following criteria in this case: (1) The URL comes from a trusted source, such as a referral server which the client has validated and trusts according to site policy. Note that user entry of the URL may or may not count as a trusted source, depending on the experience level of the user and site policy. (2) Explicit local site policy permits the client to connect to the server in the URL. For example, if the client knows the site domain name, site policy may dictate that any hostname ending in that domain is trusted. (3) The user confirms that connecting to that domain name with the specified credentials and/or mechanism is permitted. (4) A mechanism is used which validates the server before passing potentially compromising client credentials. (5) An authentication mechanism is used which will not reveal information to the server which could be used to compromise future connections. A URL containing ";AUTH=*" should be treated with extra care since it might fall back on a weaker security mechanism. Finally, clients are discouraged from using a plain text password as a fallback with ";AUTH=*" unless the connection has strong encryption (e.g., a key length of greater than 56 bits). Note that if unsafe or reserved characters such as " " or ";" are present in the user name or authentication mechanism, they MUST be encoded as described in RFC 1738 [BASIC-URL]. 5. Relative POP URLs Relative POP URLs are not permitted. Gellens Expires August 1998 [Page 3]
Internet Draft POP URL Scheme February 1998 6. Multinational Considerations Since 8-bit characters are not permitted in URLs, [UTF8] characters are encoded as required by the URL specification [BASIC-URL]. 7. Examples The following examples demonstrate how a POP client program might translate various POP URLs into a series of POP commands. Commands sent from the client to the server are prefixed with "C:", and responses sent from the server to the client are prefixed with "S:". The URL: <pop:rg@mailsrv.qualcomm.com> Results in the following client commands: <request password from user> <connect to mailsrv.qualcomm.com, port 110> S: +OK POP3 server ready <1896.697170952@mailsrv.qualcomm.com> C: USER rg S: +OK C: PASS secret S: +OK rg's mailbox has 2 messages (320 octets) The URL: <pop:rg;AUTH=APOP@mail.eudora.com:8110> Results in the following client commands: <client requests password from user> <connect to mail.eudora.com, port 8110> S: +OK POP3 server ready <1896.697170952@mail.eudora.com> C: APOP rg c4c9334bac560ecc979e58001b3e22fb S: +OK mailbox has 1 message (369 octets) The URL: <pop:baz;AUTH=SCRAM-MD5@foo.bar> Results in the following client commands: <connect to foo.bar, port 110> S: +OK POP3 server ready <1896.697170952@foo.bar> C: AUTH SCRAM-MD5 AGNocmlzADx0NG40UGFiOUhCMEFtL1FMWEI3MmVnQGVsZW Fub3IuaW5ub3NvZnQuY29tPg== S: + dGVzdHNhbHQBAAAAaW1hcEBlbGVhbm9yLmlubm9zb2Z0LmNvbQBq aGNOWmxSdVBiemlGcCt2TFYrTkN3 Gellens Expires August 1998 [Page 4]
Internet Draft POP URL Scheme February 1998 C: AQAAAMg9jU8CeB4KOfk7sUhSQPs= S: + U0odqYw3B7XIIW0oSz65OQ== C: S: +OK mailbox has 1 message (369 octets) 8. ABNF for POP URL scheme The POP URL scheme is described using [ABNF]: achar = uchar / "&" / "=" / "~" ; see [BASIC-URL] for "uchar" definition auth = ";AUTH=" ( "*" / enc_auth_type ) enc_auth_type = 1*achar ; encoded version of [POP-AUTH] "auth_type" enc_user = 1*achar ; encoded version of [POP3] mailbox popurl = "pop://" server server = [userauth "@"] hostport ; See [BASIC-URL] for "hostport" definition userauth = enc_user [auth] 9. Security Considerations Security considerations discussed in the [POP3] specification and the [BASIC-URL] specification are relevant. Security considerations related to authenticated URLs are discussed in section 4 of this document. Many email clients store the plain text password for later use after logging into a POP server. Such clients MUST NOT use a stored password in response to a POP URL without explicit permission from the user to supply that password to the specified host name. 10. Acknowledgements This document borrows heavily from Chris Newman's [IMAP-URL] specification, and has attempted to follow the advice in [URL-GUIDELINES]. Gellens Expires August 1998 [Page 5]
Internet Draft POP URL Scheme February 1998 11. References [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd., November 1997. <ftp://ds.internic.net/rfc/rfc2234.txt> [ACAP] Newman, Myers, "ACAP -- Application Configuration Access Protocol", RFC 2244, Innosoft, Netscape, November 1997. <ftp://ds.internic.net/rfc/rfc2244.txt> [BASIC-URL] Berners-Lee, Masinter, McCahill, "Uniform Resource Locators (URL)", RFC 1738, CERN, Xerox Corporation, University of Minnesota, December 1994. <ftp://ds.internic.net/rfc/rfc1738.txt> [IMAP-URL] Newman, C., "IMAP URL Scheme", RFC 2192, Innosoft, September 1997. <ftp://ds.internic.net/rfc/rfc2192.txt> [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 2060, University of Washington, December 1996. <ftp://ds.internic.net/rfc/rfc2060.txt> [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997. <ftp://ds.internic.net/rfc/rfc2119.txt> [POP-AUTH] Myers, J., "POP3 AUTHentication command", Netscape Communications, November 1997, work in progress. <ftp://ftp.isi.edu/internet-drafts/draft-myers-sasl-pop3-02.txt> [POP3] Myers, J., Rose, M., "Post Office Protocol -- Version 3", RFC 1939, Carnegie Mellon, Dover Beach Consulting, Inc., May 1996. <ftp://ds.internic.net/rfc/rfc1939.txt> [URL-GUIDELINES] Masinter, Alvestrand, Zigmond, "Guidelines for new URL Schemes", Xerox Corporation, UNINETT A/S, Wink Communications, work in progress, December 1997. <ftp://ftp.isi.edu/internet-drafts/draft-ietf-urlreg-guide-01.txt> [UTF8] Yergeau, F. "UTF-8, a transformation format of Unicode and ISO 10646", RFC 2044, Alis Technologies, October 1996. <ftp://ds.internic.net/rfc/rfc2044.txt> 12. Author's Address Randall Gellens +1 619 651 5115 QUALCOMM, Incorporated +1 619 651 5334 (fax) 6455 Lusk Blvd. Randy@Qualcomm.Com San Diego, CA 92121-2779 U.S.A. Gellens Expires August 1998 [Page 6]