public function loadFile($filename)
    {
        foreach (file($filename, FILE_IGNORE_NEW_LINES) as $line) {
            if (2 !== substr_count($line, ':')) {
                throw new DAV\Exception('Malformed htdigest file. Every line should contain 2 colons');
            }
            list($username, $realm, $A1) = explode(':', $line);

            if (!preg_match('/^[a-zA-Z0-9]{32}$/', $A1)) {
                throw new DAV\Exception('Malformed htdigest file. Invalid md5 hash');
            }
            $this->users[$realm.':'.$username] = $A1;
        }
    }