public function auth($uid, $pwd , $method = '', $tls = true, $authz = '')
    {
        /* We can only attempt a TLS connection if one has been requested,
         * we're running PHP 5.1.0 or later, have access to the OpenSSL
         * extension, are connected to an SMTP server which supports the
         * STARTTLS extension, and aren't already connected over a secure
         * (SSL) socket connection. */
        if ($tls && version_compare(PHP_VERSION, '5.1.0', '>=')
            && extension_loaded('openssl') && isset($this->esmtp['STARTTLS'])
            && strncasecmp($this->host, 'ssl://', 6) !== 0
        ) {
            /* Start the TLS connection attempt. */
            if (PEAR::isError($result = $this->put('STARTTLS'))) {
                return $result;
            }
            if (PEAR::isError($result = $this->parseResponse(220))) {
                return $result;
            }
            if (isset($this->socket_options['ssl']['crypto_method'])) {
                $crypto_method = $this->socket_options['ssl']['crypto_method'];
            } else {
                /* STREAM_CRYPTO_METHOD_TLS_ANY_CLIENT constant does not exist
                 * and STREAM_CRYPTO_METHOD_SSLv23_CLIENT constant is
                 * inconsistent across PHP versions. */
                $crypto_method = STREAM_CRYPTO_METHOD_TLS_CLIENT
                                 | @STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT
                                 | @STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT;
            }
            if (PEAR::isError($result = $this->socket->enableCrypto(true, $crypto_method))) {
                return $result;
            } elseif ($result !== true) {
                return PEAR::raiseError('STARTTLS failed');
            }

            /* Send EHLO again to recieve the AUTH string from the
             * SMTP server. */
            $this->negotiate();
        }

        if (empty($this->esmtp['AUTH'])) {
            return PEAR::raiseError('SMTP server does not support authentication');
        }

        /* If no method has been specified, get the name of the best
         * supported method advertised by the SMTP server. */
        if (empty($method)) {
            if (PEAR::isError($method = $this->getBestAuthMethod())) {
                /* Return the PEAR_Error object from _getBestAuthMethod(). */
                return $method;
            }
        } else {
            $method = strtoupper($method);
            if (!array_key_exists($method, $this->auth_methods)) {
                return PEAR::raiseError("$method is not a supported authentication method");
            }
        }

        if (!isset($this->auth_methods[$method])) {
            return PEAR::raiseError("$method is not a supported authentication method");
        }

        if (!is_callable($this->auth_methods[$method], false)) {
            return PEAR::raiseError("$method authentication method cannot be called");
        }

        if (is_array($this->auth_methods[$method])) {
            list($object, $method) = $this->auth_methods[$method];
            $result = $object->{$method}($uid, $pwd, $authz, $this);
        } else {
            $func   = $this->auth_methods[$method];
            $result = $func($uid, $pwd, $authz, $this);
        }

        /* If an error was encountered, return the PEAR_Error object. */
        if (PEAR::isError($result)) {
            return $result;
        }

        return true;
    }