<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.gdata.authsub">
    <title>Authenticating with AuthSub</title>

    <para>
        The AuthSub mechanism enables you to write web applications
        that acquire authenticated access Google Data services,
        without having to write code that handles user credentials.
    </para>

    <para>
        See <ulink
            url="http://code.google.com/apis/accounts/AuthForWebApps.html">http://code.google.com/apis/accounts/AuthForWebApps.html</ulink>
        for more information about Google Data AuthSub authentication.
    </para>

    <para>
        The Google documentation says the ClientLogin mechanism is appropriate
        for "installed applications" whereas the AuthSub mechanism is
        for "web applications." The difference is that AuthSub requires
        interaction from the user, and a browser interface that can react
        to redirection requests. The ClientLogin solution uses <acronym>PHP</acronym> code to
        supply the account credentials; the user is not required to enter her
        credentials interactively.
    </para>

    <para>
        The account credentials supplied via the AuthSub mechanism are
        entered by the user of the web application. Therefore they must be
        account credentials that are known to that user.
    </para>

    <note>
        <title>Registered applications</title>

        <para>
            <classname>Zend_Gdata</classname> currently does not support use of secure tokens,
            because the AuthSub authentication does not support passing a digital certificate
            to acquire a secure token.
        </para>
    </note>

    <sect2 id="zend.gdata.authsub.login">
        <title>Creating an AuthSub authenticated Http Client</title>

        <para>
            Your <acronym>PHP</acronym> application should provide a hyperlink to the
            Google <acronym>URL</acronym> that performs authentication. The static function
            <methodname>Zend_Gdata_AuthSub::getAuthSubTokenUri()</methodname>
            provides the correct <acronym>URL</acronym>. The arguments to this function include
            the <acronym>URL</acronym> to your <acronym>PHP</acronym> application so that Google can
            redirect the user's browser back to your application after the user's
            credentials have been verified.
        </para>

        <para>
            After Google's authentication server redirects the user's browser
            back to the current application, a <constant>GET</constant> request parameter is set,
            called <emphasis>token</emphasis>. The value of this parameter is a single-use token
            that can be used for authenticated access. This token can be converted into a multi-use
            token and stored in your session.
        </para>

        <para>
            Then use the token value in a call to
            <methodname>Zend_Gdata_AuthSub::getHttpClient()</methodname>.
            This function returns an instance of <classname>Zend_Http_Client</classname>,
            with appropriate headers set so that subsequent requests your
            application submits using that <acronym>HTTP</acronym> Client are also authenticated.
        </para>

        <para>
            Below is an example of <acronym>PHP</acronym> code for a web application
            to acquire authentication to use the Google Calendar service
            and create a <classname>Zend_Gdata</classname> client object using that authenticated
            <acronym>HTTP</acronym> Client.
        </para>

        <programlisting language="php"><![CDATA[
$my_calendar = 'http://www.google.com/calendar/feeds/default/private/full';

if (!isset($_SESSION['cal_token'])) {
    if (isset($_GET['token'])) {
        // You can convert the single-use token to a session token.
        $session_token =
            Zend_Gdata_AuthSub::getAuthSubSessionToken($_GET['token']);
        // Store the session token in our session.
        $_SESSION['cal_token'] = $session_token;
    } else {
        // Display link to generate single-use token
        $googleUri = Zend_Gdata_AuthSub::getAuthSubTokenUri(
            'http://'. $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'],
            $my_calendar, 0, 1);
        echo "Click <a href='$googleUri'>here</a> " .
             "to authorize this application.";
        exit();
    }
}

// Create an authenticated HTTP Client to talk to Google.
$client = Zend_Gdata_AuthSub::getHttpClient($_SESSION['cal_token']);

// Create a Gdata object using the authenticated Http Client
$cal = new Zend_Gdata_Calendar($client);
]]></programlisting>
    </sect2>

    <sect2 id="zend.gdata.authsub.logout">
        <title>Revoking AuthSub authentication</title>

        <para>
            To terminate the authenticated status of a given token, use the
            <methodname>Zend_Gdata_AuthSub::AuthSubRevokeToken()</methodname>
            static function. Otherwise, the token is still valid for
            some time.
        </para>

        <programlisting language="php"><![CDATA[
// Carefully construct this value to avoid application security problems.
$php_self = htmlentities(substr($_SERVER['PHP_SELF'],
                         0,
                         strcspn($_SERVER['PHP_SELF'], "\n\r")),
                         ENT_QUOTES);

if (isset($_GET['logout'])) {
    Zend_Gdata_AuthSub::AuthSubRevokeToken($_SESSION['cal_token']);
    unset($_SESSION['cal_token']);
    header('Location: ' . $php_self);
    exit();
}
]]></programlisting>

        <note>
            <title>Security notes</title>

            <para>
                The treatment of the <varname>$php_self</varname> variable in the
                example above is a general security guideline, it is not
                specific to <classname>Zend_Gdata</classname>. You should always filter content you
                output to <acronym>HTTP</acronym> headers.
            </para>

            <para>
                Regarding revoking authentication tokens, it is recommended to
                do this when the user is finished with her Google Data session.
                The possibility that someone can intercept the token and use
                it for malicious purposes is very small, but nevertheless it is
                a good practice to terminate authenticated access to any service.
            </para>
        </note>
    </sect2>
</sect1>
