Master users/passwords
======================

It's possible to configure master users who are able to log in as other users.
It's also possible to directly log in as any user using a master password,
although this isn't recommended.

Master users
------------

There are two ways for master users to log in as other users:

 1. Give the login username in the <SASL mechanism's>
    [Authentication.Mechanisms.txt] authorization ID field. Currently only the
    PLAIN SASL mechanism supports this.
 2. Specify both the master username and the login username in the same
    username field. The usernames are separated by a string configured by the
    'auth_master_user_separator' setting. UW-IMAP uses "*" as the separator, so
    that could be a good choice. Using "*" as the separator, the master user
    would log in as "login_user*master_user".

Master users are configured by adding a new <passdb> [PasswordDatabase.txt]
with 'master=yes' setting. The users in the master passdb cannot log in as
themselves, only as other people. That means they don't need to exist in the
<userdb> [UserDatabase.txt], because the userdb lookup is done only for the
user they're logging in as.

You should also add the 'pass=yes' setting to the master passdb if possible. It
means that Dovecot verifies that the login user really exists before allowing
the master user to log in. Without the setting if a non-existing login username
is given, depending on the configuration, it could either return an internal
login error (the userdb lookup failed) or create a whole new user (with eg.
<static userdb> [UserDatabase.Static.txt]). 'pass=yes' doesn't work with PAM or
LDAP with 'auth_bind=yes', because both of them require knowing the user's
password.

'pass=yes' is especially useful with a <Checkpassword>
[PasswordDatabase.CheckPassword.txt] passdb because the script gets both the
login and the master username as environment variables. Other passdbs see only
the login username in '%u'. In the future there will probably be another
setting to make the user verification to be done from userdb.

If you want master users to be able to log in as themselves, you'll need to
either add the user to the normal passdb or add the passdb to 'dovecot.conf'
twice, with and without 'master=yes'. Note that if the passdbs point to
different locations, the user can have a different password when logging in as
other users than when logging in as himself. This is a good idea since it can
avoid accidentally logging in as someone else.

Usually it's better to have only a few special master users that are used
*only* to log in as other people. One example could be a special "spam" master
user that trains the users' spam filters by reading the messages from the
user's spam mailbox.

Example configuration
---------------------

---%<-------------------------------------------------------------------------
auth_master_user_separator=*
auth default {
  passdb passwd-file {
    args = /etc/dovecot/passwd.masterusers
    master = yes
    pass = yes
  }
  passdb shadow {
  }
  userdb passwd {
  }
}
---%<-------------------------------------------------------------------------

Where the 'passwd.masterusers' file would contain the master usernames and
passwords:

---%<-------------------------------------------------------------------------
admin:{SHA1}nU4eI71bcnBGqeO0t9tXvY1u5oQ=
admin2:{SHA1}i+UhJqb95FCnFio2UdWJu1HpV50=
---%<-------------------------------------------------------------------------

One way to create this master file is to use the htaccess program as follows:

---%<-------------------------------------------------------------------------
htpasswd -b -c -s passwd.masterusers user password
---%<-------------------------------------------------------------------------

SQL Example
-----------

The master passdb doesn't have to be passwd-file, it could be an SQL query as
well:

---%<-------------------------------------------------------------------------
auth_master_user_separator=*
auth default {
  passdb sql {
    args = /etc/dovecot/dovecot-sql-master.conf
    master = yes
    pass = yes
  }
  passdb sql {
    args = /etc/dovecot/dovecot-sql.conf
  }
  userdb sql {
    args = /etc/dovecot/dovecot-sql.conf
  }
}
---%<-------------------------------------------------------------------------

'dovecot-sql-master.conf' would contain all the normal connection settings and
a 'password_query':

---%<-------------------------------------------------------------------------
password_query = SELECT password FROM users WHERE userid = '%u' and master_user
= true
---%<-------------------------------------------------------------------------

Testing
-------

---%<-------------------------------------------------------------------------
# telnet localhost 143
* OK Dovecot ready.
1 login loginuser*masteruser masterpass
1 OK Logged in.
---%<-------------------------------------------------------------------------

If you had any problems, set 'auth_debug=yes' and look at the logs.

Master passwords
----------------

The easiest way to implement this is with SQL:

---%<-------------------------------------------------------------------------
password_query = SELECT user, 'master-password' AS password FROM users WHERE
userid = '%u'
---%<-------------------------------------------------------------------------

If you don't have the users in SQL database, you can still fake it:

---%<-------------------------------------------------------------------------
password_query = SELECT '%u' AS user, 'master-password' AS password
---%<-------------------------------------------------------------------------

However note that the above will allow logins for any username using the master
password, even those that don't really exist.

Then in your dovecot.conf, have something like:

---%<-------------------------------------------------------------------------
auth default {
..
  passdb pam {
  }
  passdb sql {
    args = /etc/dovecot-sql-master.conf
  }
..
}
---%<-------------------------------------------------------------------------

One way to do this without SQL is to create a <passwd-file>
[AuthDatabase.PasswdFile.txt] containing every user:

---%<-------------------------------------------------------------------------
user1:{plain}master-password
user2:{plain}master-password
..etc..
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2010-05-24 04:42)
