<?php
   function auth($user_id="", $password="")
   {
      //check for alphanumeric only characters in username
      $pattern = '/^[a-zA-Z0-9]+$/';
      if(!preg_match($pattern,$user_id))
      {
         $realm = $_SERVER['SERVER_NAME'];
         header("WWW-Authenticate: Basic realm=\"$realm\"");
         header('HTTP/1.0 401 Unauthorized');
         echo 'Authorization Required';
         exit;
      }
       
      //check for characters in password allow (! through ~ only)
      $pattern = '/^[!-~]+$/';
      if(!preg_match($pattern,$password))
      {
         $realm = $_SERVER['SERVER_NAME'];
         header("WWW-Authenticate: Basic realm=\"$realm\"");
         header('HTTP/1.0 401 Unauthorized');
         echo 'Authorization Required';
         exit;
      }    
                  
      if (isset($user_id) and isset($password))
      {
         //--------------------------------------------------------------------
         // Establish a connection to the authorization database
         //--------------------------------------------------------------------
         $connect = mysql_connect(***, ***, ***)
            or die("Could not connect: " . mysql_error());
         mysql_select_db("authorization")
            or die("Unable to select database!");

         $user_query = "select project.name " .
                       "from authorization, user, project, roles " .
                       "where user.user_id = authorization.user_id and " .
                       "      user.user_id = '" . mysql_real_escape_string($user_id) . "' and " .
                       "      user.password = '" . mysql_real_escape_string($password) . "' and " .
                       "      project.id = project_id and " .
                       "      roles.id = role_id " .
                       "limit 1";

         $user_result = mysql_query($user_query);
         mysql_close($connect);
         $valid = mysql_numrows($user_result) > 0;
      }
      if (!$valid)
      {
         $realm = $_SERVER['SERVER_NAME'];
         header("WWW-Authenticate: Basic realm=\"$realm\"");
         header('HTTP/1.0 401 Unauthorized');
         echo 'Authorization Required';
         exit;
      }
   }
?>