PHP/Login Authentication/Authentication

Authenticate user: Database based

<?php
   function authenticate_user() {
      header("WWW-Authenticate: Basic realm="Secret Stash"");
      header("HTTP/1.0 401 Unauthorized");
      exit;
   }
   if (! isset($_SERVER["PHP_AUTH_USER"])) {
      authenticate_user();
   } else {
      mysql_pconnect("localhost","authenticator","secret") or die("Can"t connect to database server!");
      mysql_select_db("wbex") or die("Can"t select authentication database!");
      $query = "SELECT username, pswd FROM user WHERE username="$_SERVER[PHP_AUTH_USER]" AND pswd=MD5("$_SERVER[PHP_AUTH_PW]")";
      $result = mysql_query($query);
      // If nothing was found, reprompt the user for the login information.
      if (mysql_num_rows($result) == 0) {
         authenticate_user();
      }
   }
?>