Lua based authentication

New in version v2.3.0.

You can implement passdb and userdb using Lua script.

Known bugs

• Before 2.3.4 when returning a table with values, the table values are mistakenly converted into a number if they seem like a number. So if you are using values like 012345, this would get converted into 12345

• Before 2.3.4 returning password without scheme would cause a crash.

Lua based authentication

When used in authentication, additional module dovecot.auth is added, which contains constants for passdb and userdb.

For details about Dovecot Lua, see Dovecot Lua Support.

When used in authentication, additional module dovecot.auth is added, which contains constants for passdb and userdb.

List of constants

• dovecot.auth.PASSDB_RESULT_INTERNAL_FAILURE

• dovecot.auth.PASSDB_RESULT_SCHEME_NOT_AVAILABLE - indicates password scheme that cannot be understood

• dovecot.auth.PASSDB_RESULT_USER_UNKNOWN

• dovecot.auth.PASSDB_RESULT_USER_DISABLED

• dovecot.auth.PASSDB_RESULT_PASS_EXPIRED

• dovecot.auth.PASSDB_RESULT_NEXT - indicates that this passdb did not authenticate user, next passdb should do it

• dovecot.auth.PASSDB_RESULT_PASSWORD_MISMATCH

• dovecot.auth.PASSDB_RESULT_OK

• dovecot.auth.USERDB_RESULT_INTERNAL_FAILURE

• dovecot.auth.USERDB_RESULT_USER_UNKNOWN

• dovecot.auth.USERDB_RESULT_OK

Also, it registers object struct auth_request* which lets access various parts of the auth request. You should use the loggers associated with auth_request when possible.

Auth request methods

Functions:

• auth_request#log_debug(text) - logs debug message (if debug is enabled, noop otherwise)

• auth_request#log_error(text) - logs error message

• auth_request#log_info(text) - logs informational message

• auth_request#log_warning(text) - logs warning message

• auth_request#response_from_template(template) - takes in key=value template and expands it using var_expand and produces table suitable for passdb result

• auth_request#var_expand(template) - performs var expansion on the template using Config Variables

• auth_request#password_verify(crypted_password, plain_password) - checks if the plain password matches the crypted or hashed password

• auth_request#event() - Returns child event for the auth request, can be used for logging and other events. Comes with a prefix.

  New in version v2.3.7.

Subtables:

• auth_request#passdb

• auth_request#userdb

Members:

See Config Variables for details.

• auth_request#auth_domain

• auth_request#auth_user

• auth_request#auth_username

• auth_request#cert

• auth_request#client_id

• auth_request#domain

• auth_request#domain_first

• auth_request#domain_last

• auth_request#home

• auth_request#lip

• auth_request#local_name

• auth_request#login_domain

• auth_request#login_user

• auth_request#login_username

• auth_request#lport

• auth_request#master_user

• auth_request#mech

• auth_request#orig_domain

• auth_request#orig_user

• auth_request#orig_username

• auth_request#password

• auth_request#pid

• auth_request#real_lip

• auth_request#real_lport

• auth_request#real_rip

• auth_request#real_rport

• auth_request#rip

• auth_request#rport

• auth_request#secured

• auth_request#service

• auth_request#session

• auth_request#session_pid

• auth_request#user

• auth_request#username

Additionally you can access

• skip_password_check - Set if the password has already been validated by another passdb

• passdbs_seen_user_unknown - If some previous passdb has not found this user

• passdbs_seen_internal_failure - If some previous passdb has had internal failure

• userdbs_seen_internal_failure - If some previous userdb has had internal failure

Password database

Lua passdb supports two modes of function. It can behave as lookup database, or password verification database.

Lookup function signature is auth_passdb_lookup(request) and the password verification signature is auth_password_verify(request, password)

Both functions must return a tuple, which contains a return code, and also additionally string or table. Table must be in key-value format, it will be imported into auth request. The string must be in key=value format, except if return code indicates internal error, the second parameter can be used as error string.

If auth_password_verify is found, it’s always used.

To configure passdb in dovecot, use

passdb {
  driver = lua
  args = file=/path/to/lua blocking=yes # default is yes
}

By default, dovecot runs Lua scripts in auth-worker processes. If you do not want this, you can disable blocking, and Lua script will be ran in auth process. This can degrade performance if your script is slow or makes external lookups.

User database

Lua userdb supports both single user lookup and iteration. Note that iteration will hold the whole user database in memory during iteration.

User lookup function signature is auth_userdb_lookup(request). The function must return a tuple, which contains a return code, and also additionally string or table. Table must be in key-value format, it will be imported into auth request. The string must be in key=value format, except if return code indicates internal error, the second parameter can be used as error string.

User iteration function signature is auth_userdb_iterate, which is expected to return table of usernames. Key names are ignored.

Lua userdb supports both single user lookup and iteration.

Note

The iteration will hold the whole user database in memory during iteration.

To configure userdb in dovecot, use

userdb {
  driver = lua
  args = file=/path/to/lua blocking=yes # default is yes
}

Examples

function auth_passdb_lookup(req)
  if req.user == "testuser1" then
    return dovecot.auth.PASSDB_RESULT_OK, "password=pass"
  end
  return dovecot.auth.PASSDB_RESULT_USER_UNKNOWN, "no such user"
end

function auth_userdb_lookup(req)
  if req.user == "testuser1" then
    return dovecot.auth.USERDB_RESULT_OK, "uid=vmail gid=vmail"
  end
  return dovecot.auth.USERDB_RESULT_USER_UNKNOWN, "no such user"
end

function script_init()
  return 0
end

function script_deinit()
end

function auth_userdb_iterate()
  return {"testuser1"}
end

Simple username password database (such as opensmtpd)

The example uses whitespace separated username and password. As a special caution, the way Lua is used here means you can have multiple user password per line, instead of just one. This can be extended to more complicated separators or multiple fields per user.

If you only want to authenticate users, and don’t care about user listing, you can use

function auth_passdb_lookup(req)
   for line in io.lines("/path/to/file") do
       for user, pass in string.gmatch(line, "(%w+)%s(.+)") do
           if (user == req.username) then
               -- you can add additional information here, like userdb_uid
               return dovecot.auth.PASSDB_RESULT_OK, "password=" .. pass
           end
       end
   end
   return dovecot.auth.PASSDB_RESULT_USER_UNKNOWN, ""
end

If you also want to be able to list users, so that you could use doveadm cmd -A

local database = "/path/to/file"

function db_lookup(username)
   for line in io.lines(database) do
       for user, pass in string.gmatch(line, "(%w+)%s(.+)") do
           if (user == username) then
               return {result=0, password=pass}
           end
       end
   end
   return {result=-1}
end

function auth_passdb_lookup(req)
   res = db_lookup(req.username)
   if res.result == 0 then
       -- you can add additional information here for passdb
       return dovecot.auth.PASSDB_RESULT_OK, "password=" .. res.password
   end
   return dovecot.auth.PASSDB_RESULT_USER_UNKNOWN, ""
end

function auth_userdb_lookup(req)
   res = db_lookup(req.username)
   if res.result == 0 then
       -- you can add additional information here for userdb, like uid or home
       return dovecot.auth.USERDB_RESULT_OK, "uid=vmail gid=vmail"
   end
   return dovecot.auth.USERDB_RESULT_USER_UNKNOWN, ""
end

function auth_userdb_iterate()
  users = {}
  for line in io.lines(database) do
       for user in string.gmatch(line, "(%w+)%s.+") do
           table.insert(users, user)
       end
  end
  return users
end