Using a PHP Script on an Apache Server as the IMAP Auth Backend

Start with the configuration from IMAP Proxy Example. For detailed information about different configuration parameters, see the ngx_mail_core_module page.

  1. Your Proxy server for pop/imap is running on 192.168.1.1
  2. You have 2 backend pop/imap servers: 192.168.1.22 and 192.168.1.33
  3. You have a webserver that you will use for the authentication and redirection logic 192.168.1.44.
  4. The authentication script is /mail/auth.php

nginx.conf

user  nobody;
worker_processes  1;
error_log  logs/error.log  info;
pid  logs/nginx.pid;

events {
  worker_connections  1024;
  multi_accept on;
}

mail {
  auth_http  192.168.1.44:80/mail/auth.php;
  pop3_capabilities  "TOP"  "USER";
  imap_capabilities  "IMAP4rev1"  "UIDPLUS";

  server {
    listen     110;
    protocol   pop3;
    proxy      on;
  }

  server {
    listen     143;
    protocol   imap;
    proxy      on;
  }
}

/mail/auth.php

<?php
/*
NGINX sends headers as
Auth-User: somuser
Auth-Pass: somepass
On my php app server these are seen as
HTTP_AUTH_USER and HTTP_AUTH_PASS
*/
if (!isset($_SERVER["HTTP_AUTH_USER"] ) || !isset($_SERVER["HTTP_AUTH_PASS"] )){
  fail();
}

$username=$_SERVER["HTTP_AUTH_USER"] ;
$userpass=$_SERVER["HTTP_AUTH_PASS"] ;
$protocol=$_SERVER["HTTP_AUTH_PROTOCOL"] ;

// default backend port
$backend_port=110;

if ($protocol=="imap") {
  $backend_port=143;
}

if ($protocol=="smtp") {
  $backend_port=25;
}

// NGINX likes ip address so if your
// application gives back hostname, convert it to ip address here
$backend_ip["mailhost01"] ="192.168.1.22";
$backend_ip["mailhost02"] ="192.168.1.33";

// Authenticate the user or fail
if (!authuser($username,$userpass)){
  fail();
  exit;
}

// Get the server for this user if we have reached so far
$userserver=getmailserver($username);

// Get the ip address of the server
// We are assuming that you backend returns hostname
// We try to get the ip else return what we got back
$server_ip=(isset($backend_ip[$userserver]))?$backend_ip[$userserver] :$userserver;

// Pass!
pass($server_ip, $backend_port);

//END

function authuser($user,$pass){
  // put your logic here to authen the user to any backend
  // you want (datbase, ldap, etc)
  // for example, we will just return true;
  return true;
}

function getmailserver($user){
  // put the logic here to get the mailserver
  // backend for the user. You can get this from
  // some database or ldap etc
  // dummy logic, all users that start with a,c,f and g get mailhost01
  // the others get mailhost02
  if in_array(substr($user,0,1), array("a", "c", "f", "g")){
    return "mailhost01";
  } else {
    return "mailhost02";
  }
}

function fail(){
  header("Auth-Status: Invalid login or password");
  exit;
}

function pass($server,$port){
  header("Auth-Status: OK");
  header("Auth-Server: $server");
  header("Auth-Port: $port");
  exit;
}