AuthenticatedSmtpUsingSaslauthd

Nigel Metheringham edited this page Nov 25, 2012 · 1 revision
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Authenticated SMTP using SASLAuthd

Introduction

One of the options Exim has for authentication without root access is by using SASLAuthd from the Cyrus suite. This is the preferred method from the deprecated pwcheck authenticator. It is recommended you follow the instructions in the AuthenticatedSmtpUsingPam tutorial regarding encryption (TLS) as they won't be discussed here. This is based on a Gentoo install.

Required Software

  • Exim 4.x
  • Cyrus-SASL 2.x

Compiling Exim

Ensure that authentication by saslauthd is enabled in Exim. This is done in Local/Makefile:

AUTH_PLAINTEXT=yes
CYRUS_SASLAUTHD_SOCKET=/var/lib/sasl2/mux

Configuring SASLAuthd

The default arguments for SASLAuthd are contained in /etc/conf.d/saslauthd for Gentoo. Instead of using the PAM module, we'll directly access the shadow file:

SASLAUTHD_OPTS="-a shadow"

You should add that argument to where ever your distribution requires it.

Sometimes the permissions are wrong on the socket file (unknown as to why). Verify that your socket's directory (default is /var/lib/sasl2 for this ebuild) is executable by all:

chmod o+x /var/lib/sasl2

Configuring Exim

If you're using encryption (and I'm sure you are) then you'll already have an auth_advertise_hosts line that tests for such. If not, this must go in your config file to allow all hosts to authenticate:

auth_advertise_hosts = *

Now you'll want to add your authenticators:

begin authenticators

plain:
  driver = plaintext
  public_name = PLAIN
  server_prompts = :
  server_set_id = $2
  server_condition = ${if saslauthd{{$2}{$3}}{1}{0}}
  server_advertise_condition = true

login:
  driver = plaintext
  public_name = LOGIN
  server_prompts = "Username:: : Password::"
  server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}
  server_set_id = $1
  server_advertise_condition = true

Conclusion

You'll now be able to authenticate without rooting up or messing with PAM modules.

Common Errors

435 Unable to authenticate at present

Your saslauthd socket is probably set wrong in your Local/Makefile before compiling Exim.

CYRUS_SASLAUTHD_SOCKET=/var/lib/sasl2/mux

openpam_read_chain(): /etc/pam.d/(1): invalid facility '^^_^S' (ignored)

If the saslauthd PAM mech is used with OpenPAM (netBSD, FreeBSD) this error occurs in some cases.

You have to provide a service name (like "smtp" in this case points to "/etc/pam.d/smtp") to saslauthd in your config by using:

server_condition = ${if saslauthd{{$1}{$2}{smtp}}{1}{0}}

instead of

server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}

(May be this is a good idea in other situations too or should be generally added to the upper Exim config?)

535 Incorrect authentication data

SASLAuthd was unable to authenticate that user/pass combo. If you're certain it's correct, make sure the permissions are correct on your socket file's directory:

chmod o+x /var/lib/sasl2

...and that saslauthd is running:

ps aux | grep saslauthd

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