Code:

   1.
      <?php
   2.
      define( "DATABASE_SERVER", "localhost" );
   3.
      define( "DATABASE_USERNAME", "user" );
   4.
      define( "DATABASE_PASSWORD", "pass" );
   5.
      define( "DATABASE_NAME", "flex" );
   6.
      //connect to the database
   7.
      $mysql = mysql_connect(DATABASE_SERVER, DATABASE_USERNAME, DATABASE_PASSWORD) or die(mysql_error());
   8.
      //select the database
   9.
      mysql_select_db( DATABASE_NAME );
  10.
      //asign the data passed from Flex to variables
  11.
      $username = mysql_real_escape_string($_POST["username"]);
  12.
      $password = mysql_real_escape_string($_POST["password"]);
  13.
      //Query the database to see if the given username/password combination is valid.
  14.
      $query = "SELECT * FROM users WHERE username = "$username" AND password = "$password"";
  15.
      $result = mysql_fetch_array(mysql_query($query));
  16.
      //start outputting the XML
  17.
      $output = "<loginsuccess>";
  18.
      //if the query returned true, the output <loginsuccess>yes</loginsuccess> else output <loginsuccess>no</loginsuccess>
  19.
      if(!$result)
  20.
      {
  21.
      $output .= "no";           
  22.
      }else{
  23.
      $output .= "yes";     
  24.
      }
  25.
      $output .= "</loginsuccess>";
  26.
      //output all the XML
  27.
      print ($output);
  28.
      ?>