Post to Facebook stream from Apex controller

Hello.page

<apex:page controller="HelloController">
  <script src="https://connect.facebook.net/en_US/all.js"></script>
  <div id="fb-root"></div>
  <script>
    // Get required permissions from the controller
    var permissions = '{!permissions}';
    var permlist = permissions.split(',');
    var reqperms = '';
  
    FB.init({appId: '{!appId}', xfbml: true, cookie: true});
    
    // We are logged in, but we need getLoginStatus() to get the FB JS
    // lib to pick up the access token
    FB.getLoginStatus(function(response) {
      if (response.status === 'connected') {
        // Check we have the permissions we want
        FB.api('/me/permissions', function (response) {
          for (var i = 0; i < permlist.length; i++) {
              if (! response.data[0][permlist[i]]) {
                  if (reqperms !== '') {
                      reqperms += ',';
                  }
                  reqperms += permlist[i];
              }
          }
          if (reqperms.length > 0) {
            // We need some permissions - ask for them
            FB.login(function(response) {
              if (!response) {
                alert('Error getting permission!');
              } else {
                location.reload(true);
              }
            }, {scope: reqperms});
          }
        });
      } else if (response.status === 'not_authorized') {
        // The user is logged in to Facebook, 
        // but has not authenticated the app
        // We handle this in the controller
      } else {
        // The user isn't logged in to Facebook.
        // We handle this in the controller
      }
    });   
  </script>
  <apex:pageMessages />
  <apex:form>
    <apex:commandButton value="Hello" action="{!postHello}"/>
  </apex:form>
</apex:page>

HelloController.cls

public class HelloController {
    String access_token;

    public PageReference postHello() {
        Map<String,String> params = new Map<string,string>{'message' => 'Hello from Apex'};
        try {
            FacebookPublish.postToWall(access_token, 'me', params);
        } catch (FacebookException fbe) {
            ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.FATAL,
                fbe.getMessage());
            ApexPages.addMessage(myMsg);
        }
        return null;
    }

    public HelloController() {
        // Replace the ID in this call with the ID of your auth provider
        access_token = Auth.AuthToken.getAccessToken('AUTH_PROVIDER_ID', 'Facebook');
    }
    
    public String getPermissions() {
        return 'publish_stream';
    }

    public String getAppId() {
        // Replace this with your auth provider's consumer key
        return 'FACEBOOK_APP_ID';
    }  
}