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IMAP AND SMTP AUTHENTICATION WITH SQUIRRELMAIL
$Id$
Chris Hilts tassium@squirrelmail.org
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Prior to SquirrelMail 1.4.0, only plaintext logins for IMAP and SMTP were
supported.  With the release of SquirrelMail 1.4.0, support for the
CRAM-MD5 and DIGEST-MD5 auth mechanisms has been added.  TLS support has
also been added.  It is possible to use different methods for both IMAP and
SMTP. TLS is able to be enabled on a per-service basis as well.
Unless the administrator changes the authentication methods, SquirrelMail
will default to the "classic" plaintext methods, without TLS.

Note: There is no point in using TLS if your IMAP server is localhost. You need
root to sniff the loopback interface, and if you don't trust root, or an attacker
already has root, the game is over.  You've got a lot more to worry about beyond
having the loopback interface sniffed.

REQUIREMENTS
------------

CRAM/DIGEST-MD5
* SquirrelMail 1.4.0 or higher
* If you have the mhash extension to PHP, it will automatically
  be used, which may help performance on heavily loaded servers.
  ** NOTE: mhash is optional and no longer a requirement **
* Digest-MD5 authentication needs PHP XML extension.

TLS
* SquirrelMail 1.4.0 or higher
* PHP 4.3.0 or higher (Check Release Notes for PHP 4.3.x information)
* The server you wish to use TLS on must have a dedicated port listening for 
  TLS connections. (ie. port 993 for IMAP, 465 for SMTP). See STARTTLS 
  requirements, if you want to use IMAP or SMTP STARTTLS extension.
* If you use PHP 4.3.x, OpenSSL support must be compiled staticly. See
  PHP bug #29934 (http://bugs.php.net/bug.php?id=29934)

STARTTLS
* SquirrelMail 1.5.1 or higher
* PHP 5.1.0rc1 or higher (stream_socket_enable_crypto() function)
* Server with STARTTLS extension support

CONFIGURATION
-------------

All configuration is done using conf.pl, under main menu option #2.

conf.pl can now attempt to detect which mechanisms your servers support.
You must have set the host and port before attempting to detect, or you
may get inaccurate results, or a long wait while the connection times out.

If you get results that you know are wrong when you use auto-detection, send
information about it to SquirrelMail developers. Provide the results you got, 
the results you expected, and server type, name, and version (eg. "imap, 
Cyrus, v2.1.9").

KNOWN ISSUES
------------

DIGEST-MD5 has three different methods of operation. (qop options "auth",
"auth-int" and "auth-conf").  This implementation currently supports "auth"
only.  Work is being done to add the other two modes.

DIGEST-MD5 _may_ fail when authenticating with servers that supply more
than one "realm".  I have no servers of this type to test on, so if you do
and it fails, let me know!  (A big help would be for you to telnet to your
server, start a DIGEST-MD5 auth session, and include the challenge from the
server in your bug report.)

To get the challenge with IMAP:
   telnet <your server> imap
   [server says hello]
   A01 AUTHENTICATE DIGEST-MD5
   <copy the gobbledygook that the server sends - this is what I need>
   *
   [server says auth aborted]
   A02 LOGOUT
   [server says goodbye, closes connection]

To get the challenge with SMTP:
   telnet <your server> smtp
   [server sends some sort of "hello" banner]
   EHLO myhostname
   [server will probably list a bunch of capabilities]
   AUTH DIGEST-MD5
   <copy the gobbledygook that the server sends - this is what I need>
   *
   [server says auth aborted]
   QUIT
   [server says bye, closes connection]


OPTIONAL SMTP AUTH CONFIGURATION
--------------------------------

In SMTP authentication SquirrelMail uses user's login name and password. If you 
need all users to send mail via an upstream SMTP provider (your ISP, for 
example), and that ISP requires authentication, you can configure custom 
username and password. $smtp_sitewide_user configuration variable stores custom
username used during SMTP authentication. $smtp_sitewide_pass stores custom
password that is used during SMTP authentication, if $smtp_sitewide_user 
variable is not empty.

SquirrelMail 1.5.0 and 1.5.1 stored these configuration variables in 
config_local.php. Newer SquirrelMail versions allow to configure them in conf.pl
configuration utility.

These configuration variables will be used to connect to the SMTP server as long
as the authentication mechanism is something besides 'none', i.e. 'login', 
'plain', 'cram-md5', or 'digest-md5'.

DEBUGGING SSL ERROR MESSAGES
----------------------------

SquirrelMail disables display of PHP errors in fsockopen() and 
stream_socket_enable_crypto() function calls. These functions use PHP error
handler to display connection errors and SquirrelMail tries to handle
errors without displaying debugging information to end user. If you use TLS or
STARTTLS and get connection errors, try reproducing them in configtest.php
script or remove @ symbol from fsockopen() and stream_socket_enable_crypto()
calls in SquirrelMail scripts.

Possible error messages:
* SSL: Connection reset by peer in some script.
  Error happened in IMAP server and server dropped connection. It is possible
  that error is logged in system or imap logs.

* SSL operation failed with code 1. OpenSSL Error messages: error:14094410:SSL
routines:func(148):reason(1040) in some script.
  Error generated by SSL library. Locate numbers listed in 'SSL 
  routines:func(###):reason(####)' string, find ssl.h file in your OpenSSL
  sources and locate same numbers listed in '/* Error codes for the SSL
  functions. */' section. Error define can be self explanatory. If you don't
  understand it, search for error or that define in your favorite search
  engine.


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