Key-value authentication (dict) database

Key-value databases can be used as auth backends. They probably should be used only for caching in front of e.g. SQL auth backends. Iteration is supported if the underlying dict provider supports iteration. See Dictionary for list of supported databases.

Auth configuration

dovecot.conf:

passdb {
  driver = dict
  args = /etc/dovecot/dovecot-dict-auth.conf
}
userdb {
  driver = dict
  args = /etc/dovecot/dovecot-dict-auth.conf
}

Dict base configuration

uri = redis:host=127.0.0.1:port=6379

# Dictionary URI
#uri =

# Default password scheme
default_pass_scheme = MD5

# Username iteration prefix. Keys under this are assumed to contain usernames.
iterate_prefix = userdb/

# Should iteration be disabled for this userdb? If this userdb acts only as a
# cache there's no reason to try to iterate the (partial & duplicate) users.
#iterate_disable = no

There are two ways to access the dict (although they can also be mixed):

  • JSON string object lookups (passdb_objects, userdb_objects)

  • Individual value lookups (passdb_fields, userdb_fields)

Note that all the key lookups must either find the value or have a default_value setting specified. Otherwise the entire passdb or userdb lookup will fail as “user not found” - even if some of the keys were found.

JSON object lookups

JSON object is looked up from the dict. Its contents are added to passdb/userdb fields. Note that only the first object is automatically used. More objects can be specified, but their fields need to be explicitly referred to by passdb_fields or userdb_fields.

key passdb {
  key = passdb/%u
  format = json
}
key userdb {
  key = userdb/%u
  format = json
}

# key used for passdb lookup
passdb_objects = passdb
# key used for userdb lookup
userdb_objects = userdb

Individual value lookups

Each %{dict:key} variable expansion does a dict lookup for the key. The value is used exactly as it is in the database without any kind of parsing.

key password {
  key = passwords/%u
  #format = value # value is the default
}
key proxy_host {
  key = proxy-hosts/%u
  default_value = default.example.com
}
passdb_fields {
  proxy = yes
  host = %{dict:proxy_host}
  password = %{dict:password}
}

key quota {
  # Assumes quota_class was already set by previous userdb lookup
  key = quota/%{userdb:quota_class}
  default_value = 100M
}
userdb_fields {
  quota_rule = *:storage=%{dict:quota}
}

Mixing fields and JSON objects

It’s possible to also refer to JSON objects in the passdb_fields and userdb_fields. Although due to a bug the objects must currently be listed in passdb_objects or userdb_objects as well, which causes all of their fields to be imported.

key passdb {
  key = passdb/%u
  format = json
}
key domaindb {
  key = domaindb/%d
  format = json
  default_value = {"host": "default-backend.example.com"}
}
passdb_objects = passdb domaindb

passdb_fields {
  # password is imported from the passdb key automatically
  proxy = yes
  host = %{dict:domaindb.proxy_host} # assumes domaindb returns "proxy_host"
}

dict proxying

It may be useful to do the lookups via the dict or dict-async service. For example:

dovecot.conf:

dict {
  cassandra-userdb = cassandra:/etc/dovecot/dovecot-dict-userdb-cql.conf.ext
}

dovecot-dict-auth.conf.ext:

uri = proxy:dict-async:cassandra-userdb
iterate_disable = yes
# The _key and _path suffixes are not necessary, they're just here to help
# understand how to match them between different parts of the configuration.
key email_key {
  key = userdb/email_path/%u
}
key displayname_key {
  key = userdb/displayname_path/%u
}
userdb_fields {
  # these fields will be visible as %{userdb:u_email} and %{userdb:u_displayname}
  u_email = %{dict:email_key}
  u_displayname = %{dict:displayname_key}
}

dovecot-dict-userdb-cql.conf.ext:

driver = cassandra
connect = host=127.0.0.1 dbname=email_users

# SELECT displayname FROM user_profile WHERE id = %u
map {
  # pattern must match the "key" path, except with added shared/ prefix. %u
  # gets caught into $username
  pattern = shared/userdb/displayname_path/$username
  table = user_profile
  value_field = displayname
  value_type = string
  fields {
    id = $username
  }
}

# SELECT email FROM user_profile WHERE id = %u
map {
  pattern = shared/userdb/email_path/$username
  table = user_profile
  value_field = email
  value_type = string
  fields {
    id = $username
  }
}

Complete example for authenticating via the CDB dictionary

This example uses the CDB dictionary to store the userdb and passdb.

Auth configuration

dovecot.conf:

# Access to the CDB has to go through a dict process.
dict {
  auth = cdb:/etc/dovecot/auth.cdb
}

passdb {
  driver = dict
  args = /etc/dovecot/dovecot-cdb.conf
}

userdb {
  driver = dict
  args = /etc/dovecot/dovecot-cdb.conf
}

Dict configuration

The CDB dictionary doesn’t support iteration yet.

dovecot-cdb.conf:

uri = proxy::auth

key passdb {
   key = passdb/%u
   format = json
}
key userdb {
   key = userdb/%u
   format = json
}
# iterate_prefix = userdb/ # no yet supported
iterate_disable = yes

default_pass_scheme = BLF-CRYPT

Complete example for authenticating via a UNIX socket

The Dict auth backend can be used to query a local UNIX socket for users. This can be handy for accessing user databases which would otherwise only be accessible via the CheckPassword backend and a scripting language.

When given a proxy: URL the Dict backend speaks a simple protocol over a UNIX socket. The protocol is defined in src/lib-dict/dict-client.h (GitHub).

Auth configuration

dovecot.conf:

passdb {
  driver = dict
  args = /etc/dovecot/dovecot-dict-auth.conf
}
userdb {
  # optional
  driver = prefetch
}
userdb {
  driver = dict
  args = /etc/dovecot/dovecot-dict-auth.conf
}

Dict configuration

The last dictionary name (somewhere) argument is redundant here.

/etc/dovecot/dovecot-dict-auth.conf.ext:

uri = proxy:/var/run/auth_proxy_dovecot/socket:somewhere

# FIXME: obsolete configuration - should use the key { .. } instead
password_key = passdb/%u
user_key = userdb/%u
iterate_disable = yes
#default_pass_scheme = plain

Server process for answering Dict lookups

The server process listening on /var/run/auth_proxy_dovecot/socket can be written in any language. Here’s an example in Perl:

package AuthProxyDovecot;
use base qw( Net::Server::PreFork );

use strict;
use warnings;

use JSON::XS;

AuthProxyDovecot->run() or die "Could not initialize";

sub default_values
{
  return {
    port              => '/var/run/auth_proxy_dovecot/socket|unix',

    log_level         => 2,
    log_file          => 'Sys::Syslog',
    syslog_logsock    => 'unix',
    syslog_ident      => 'auth_proxy_dovecot',
    syslog_facility   => 'daemon',

    background        => 1,
    setsid            => 1,
    pid_file          => '/var/run/auth_proxy_dovecot.pid',

    user              => 'root',
    group             => 'root',

    max_spare_servers => 2,
    min_spare_servers => 1,
    min_servers       => 2,
    max_servers       => 10,
  };
} ## end sub default_values

##################################################

sub process_request {
  my $self   = shift;

  my %L_handler = (
      passdb => sub {
          my ($arg) = @_;
          my $ret = {
              password        => '$1$JrTuEHAY$gZA1y4ElkLHtnsrWNHT/e.',
              userdb_home     => "/home/username/",
              userdb_uid      => 1000,
              userdb_gid      => 1000,
          };
          return $ret;
      },
      userdb => sub {
          my ($arg) = @_;
          my $ret = {
              home    => "/home/username/",
              uid     => 1000,
              gid     => 1000,
          };
          return $ret;
      },
  );


 # protocol from src/lib-dict/dict-client.h
 my $json = JSON::XS->new;

 eval {
     my $ret;
     # Dict protocol is multiline... go through the lines.
     while (<STDIN>) {
         $self->log(2, "Got request: $_");
         chomp;
         my $cmd = substr($_,0,1);
         next if $cmd eq 'H'; # "hello", skip this line, assume it's ok
         die "Protocol error: Bad command $cmd" unless ($cmd eq 'L');
         # Process request

             my ($namespace,$type,$arg) = split ('/',substr($_,1),3);

             if ($namespace eq 'shared') {
                 my $f = $L_handler{$type};

                 if (defined $f && defined $arg) {
                     $ret = $f->($arg);
                 }
             } else {
                 die 'Protocol error: Bad arg';
             }
         else {
             die 'Protocol error: Bad namespace'
         }
         last; # Got an "L" , now respond.
     }
     if ($ret) {
         my $json = JSON::XS->new->indent(0)->utf8->encode($ret);
         $self->log(3,"O:$json");
         print "O".$json."\n";
     }
     else {
         $self->log(3,"NOUSER");
         print "N\n";
     }
     1;
  } or do {
     $self->log(2, "Error: $@");
     print "F\n";
  };
}

sub pre_loop_hook {
  my $self = shift;

  $self->log(1, 'Starting server');
}

sub pre_server_close_hook {
  my $self = shift;

  $self->log(1, 'Server is shut down');
}

1;

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