### -*-m4-*-
###
### Client authentication for distorted.org.uk Exim configuration
###
### (c) 2012 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

###--------------------------------------------------------------------------
### Authenticators.

m4_define(<:CHECK_PASSWD:>,
<:${lookup {$1} lsearch {CONF_sysconf_dir/passwd} \
	   {${if crypteq {$2} {$value}}} \
	   {false}}:>)

m4_define(<:ALLOW_PLAINTEXT_AUTH_P:>,
<:or {{match_ip {$sender_host_address}{+localnet}} \
      {and {{def:tls_cipher} {eq{$acl_c_mode}{submission}}}}}:>)

SECTION(auth)m4_dnl
plain:
	driver = plaintext
	public_name = PLAIN
	server_advertise_condition = ${if ALLOW_PLAINTEXT_AUTH_P}
	server_prompts = :
	server_condition = CHECK_PASSWD($auth2, $auth3)
	server_set_id = $auth2

login:
	driver = plaintext
	public_name = LOGIN
	server_advertise_condition = ${if ALLOW_PLAINTEXT_AUTH_P}
	server_prompts = <; Username: ; Password:
	server_condition = CHECK_PASSWD($auth1, $auth2)
	server_set_id = $auth1

DIVERT(null)
###--------------------------------------------------------------------------
### Verification of sender address.

SECTION(global, acl)m4_dnl
acl_not_smtp_start = not_smtp_start
SECTION(acl, misc)m4_dnl
not_smtp_start:
	## Record the user's name.
	warn	 set acl_c_user = $sender_ident

	## Done.
	accept

SECTION(acl, mail-hooks)m4_dnl
	## Check that a submitted message's sender address is allowable.
	require	 acl = mail_check_auth

SECTION(acl, misc)m4_dnl
mail_check_auth:

	## If this isn't a submission then it doesn't need checking.
	accept	 condition = ${if !eq{$acl_c_mode}{submission}}

	## If the caller hasn't formally authenticated, but this is a
	## loopback connection, then we can trust identd to tell us the right
	## answer.  So we should stash the right name somewhere consistent.
	warn	 set acl_c_user = $authenticated_id
		 hosts = +localnet
		!authenticated = *
		 set acl_c_user = $sender_ident

	## User must be authenticated.
	deny	 message = Sender not authenticated
		!hosts = +localnet
		!authenticated = *

	## Make sure that the local part is one that the authenticated sender
	## is allowed to claim.
	deny	 message = Sender address forbidden to calling user
		!condition = ${LOOKUP_DOMAIN($sender_address_domain,
			       {${if and {{match_local_part \
					    {$acl_c_user} \
					    {+dom_users}} \
					  {match_local_part \
					    {$sender_address_local_part} \
					    {+dom_locals}}}}},
			       {${if and {{match_local_part \
					    {$sender_address_local_part} \
					    {+user_extaddr}} \
					  {or {{eq {$sender_address_domain} \
						   {}} \
					       {match_domain \
						 {$sender_address_domain} \
						 {+public}}}}}}})}

	## All done.
	accept

DIVERT(null)
###--------------------------------------------------------------------------
### Dealing with `AUTH' parameters and relaying.

SECTION(global, acl)m4_dnl
acl_smtp_mailauth = mailauth
SECTION(acl, misc)m4_dnl
## Check the `AUTH=...' parameter to a `MAIL' command.
mailauth:
	## If the client has authenticated using TLS then we're OK.  The
	## sender was presumably checked upstream, and we can believe that
	## the name has been transmitted honestly.
	accept	  condition = ${if def:tls_peerdn}

	## If this is submission, and the client has authenticated, then we
	## check that the name matches the user.
	accept	  condition = ${if eq {$authenticated_sender} \
				      {$authenticated_id@CONF_master_domain}}

	## Otherwise we can't tell who really sent it.
	deny	  message = Authenticated user not authoritative for claimed sender.

DIVERT(null)
###----- That's all, folks --------------------------------------------------