// Assumes you've accepted the password
// as $password and username as $username
// prior to calling the check_auth function
function check_auth($username, $password)
{
   $host = 'somehost';
   $sqluser = 'someuser';
   $sqlpass = 'somepass';

   $good_auth = false;

   $sql = "SELECT user_password FROM db.phpbb_users WHERE username='" . $username .

"'";
   $link = mysql_connect($host, $sqluser, $sqlpass);
   if (!$link)
   {
      die("Could not connect");
   }
   $result = mysql_query($sql);
   $row = mysql_fetch_row($result);
   $dbhash = $row[0];

   $itoa64 = './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';

   if (strlen($dbhash) == 34)
   {
      $pwhash = hash_it($password, $dbhash, $itoa64);
   } else {
      $pwhash = md5($password);
   }

   if ($pwhash === $dbhash)
   {
      $good_auth = true;
   }

   return $good_auth;
}



// This is copy/paste of phpBB's
// _hash_crypt_private function
function hash_it($password, $setting, &$itoa64)
{
   $output = '*';

   // Check for correct hash
   if (substr($setting, 0, 3) != '$H$')
   {
      return $output;
   }

   $count_log2 = strpos($itoa64, $setting[3]);

   if ($count_log2 < 7 || $count_log2 > 30)
   {
      return $output;
   }

   $count = 1 << $count_log2;
   $salt = substr($setting, 4, 8);

   if (strlen($salt) != 8)
   {
      return $output;
   }

   /**
   * We're kind of forced to use MD5 here since it's the only
   * cryptographic primitive available in all versions of PHP
   * currently in use.  To implement our own low-level crypto
   * in PHP would result in much worse performance and
   * consequently in lower iteration counts and hashes that are
   * quicker to crack (by non-PHP code).
   */
   if (PHP_VERSION >= 5)
   {
      $hash = md5($salt . $password, true);
      do
      {
         $hash = md5($hash . $password, true);
      }
      while (--$count);
   }
   else
   {
      $hash = pack('H*', md5($salt . $password));
      do
      {
         $hash = pack('H*', md5($hash . $password));
      }
      while (--$count);
   }

   $output = substr($setting, 0, 12);
   $output .= _hash_encode64($hash, 16, $itoa64);

   return $output;
}

// Copy/paste of phpBB's function
function _hash_encode64($input, $count, &$itoa64)
{
   $output = '';
   $i = 0;

   do
   {
      $value = ord($input[$i++]);
      $output .= $itoa64[$value & 0x3f];

      if ($i < $count)
      {
         $value |= ord($input[$i]) << 8;
      }

      $output .= $itoa64[($value >> 6) & 0x3f];

      if ($i++ >= $count)
      {
         break;
      }

      if ($i < $count)
      {
         $value |= ord($input[$i]) << 16;
      }

      $output .= $itoa64[($value >> 12) & 0x3f];

      if ($i++ >= $count)
      {
         break;
      }

      $output .= $itoa64[($value >> 18) & 0x3f];
   }
   while ($i < $count);

   return $output;
}