当用户使用此FB按钮登录时。将生成其会话。因此，我可以使用PHP API获取我想要的任何信息。

我将此代码放在html正文中

              <script>
  window.fbAsyncInit = function() {
  FB.init({
    appId      : <?php echo $facebook->getAppId(); ?>, // App ID
    channelUrl : \'//WWW.example.com/channel.html\', // Channel File
    status     : true, // check login status
    cookie     : true, // enable cookies to allow the server to access the session
    xfbml      : true  // parse XFBML
  });

  // Here we subscribe to the auth.authResponseChange JavaScript event. This event is fired
  // for any authentication related change, such as login, logout or session refresh. This means that
  // whenever someone who was previously logged out tries to log in again, the correct case below 
  // will be handled. 
  FB.Event.subscribe(\'auth.authResponseChange\', function(response) {
    // Here we specify what we do with the response anytime this event occurs. 
    if (response.status === \'connected\') {
      // The response object is returned with a status field that lets the app know the current
      // login status of the person. In this case, we\'re handling the situation where they 
      // have logged in to the app.
      testAPI();
    } else if (response.status === \'not_authorized\') {
      // In this case, the person is logged into Facebook, but not into the app, so we call
      // FB.login() to prompt them to do so. 
      // In real-life usage, you wouldn\'t want to immediately prompt someone to login 
      // like this, for two reasons:
      // (1) JavaScript created popup windows are blocked by most browsers unless they 
      // result from direct interaction from people using the app (such as a mouse click)
      // (2) it is a bad experience to be continually prompted to login upon page load.
      FB.login();
    } else {
      // In this case, the person is not logged into Facebook, so we call the login() 
      // function to prompt them to do so. Note that at this stage there is no indication
      // of whether they are logged into the app. If they aren\'t then they\'ll see the Login
      // dialog right after they log in to Facebook. 
      // The same caveats as above apply to the FB.login() call here.
      FB.login();
    }
  });
  };

  // Load the SDK asynchronously
  (function(d){
   var js, id = \'facebook-jssdk\', ref = d.getElementsByTagName(\'script\')[0];
   if (d.getElementById(id)) {return;}
   js = d.createElement(\'script\'); js.id = id; js.async = true;
   js.src = "//connect.facebook.net/en_US/all.js";
   ref.parentNode.insertBefore(js, ref);
  }(document));

  // Here we run a very simple test of the Graph API after login is successful. 
  // This testAPI() function is only called in those cases. 
  function testAPI() {
    console.log(\'Welcome!  Fetching your information.... \');
    FB.api(\'/me\', function(response) {
      console.log(\'Good to see you, \' + response.name + \'.\');
    });
  }
</script>

        $config = array();
        $config[\'appId\'] = \'myappid\';
        $config[\'secret\'] = \'myappsecretid\';
        $config[\'fileUpload\'] = false; // optional

        $facebook = new Facebook($config);
        $access_token = FALSE;
        $user = $facebook->getUser();
        if($user){
          // The user is logged in
          try{
            $user_profile = $facebook->api(\'/me\');
            $access_token = $facebook->getAccessToken();
            // Here : API call succeeded,
            // you have a valid access token
            print_r($user_profile);  // all the user info is in this object
          }
          catch(FacebookApiException $e){
            // Here : API call failed,
            // you don\'t have a valid access token
            // you have to send him to $facebook->getLoginUrl()
            $user = null;
          }
        }