GAM - Facebook Authentication Type

This documentation is valid for:
GeneXus 18 Help

This paper is valid for GeneXus X Evolution 3 upgrade 4 and upper. For other versions see here.

[19888] provides a way to authenticate using Facebook.

Steps to follow

1. Create a "Facebook client application" in Facebook site and obtain App Id and App Secret for that application.

Go to Facebook for developers (http://developers.facebook.com/) -> My apps -> Add a new app, as shown in the following figures:

Note that you need to configure the Site URL = http://<domain> (http://apps2.genexusx.com) (eg.: apps5.genexus.com).

Note: Remember to make the FB application public

2. Define "Facebook Authentication Type" using the GAM backend. Go through Authentication Types link.

Facebook API needs the SITE URL to be different than "localhost" and the default port needs to be 80. If your application is hosted under port 8080, you need to use a proxy or similar (like Apache web server) in order to use port 80.

Important note:

In the case of Java and NET you need to enter the complete site URL in Site URL property.

For example http://apps2.genexusx.com/Ide1b858bf3b044ba0ac777119780e4370.

Never include the "/servlet" in Java.

Facebook Authentication Type can be used in Web Applications and Smart Devices applications also.

Web Applications

In the case of Web Applications, the GamExampleLogin object (which is part of the GAM - Examples) includes automatically a button by which the user can login to Facebook.
This button is included dynamically, as the Facebook Authentication Type is already defined in the GAM Repository.

The code associated to that button, which authenticates to Facebook, is as follows:

Event &ButtonFacebook.Click
    GAMRepository.LoginFacebook()
EndEvent

Considerations: The LoginFacebook function doesn't work as expected in popup windows (the same happens to LoginTwitter). This is a limitation of those sites, who don't support a redirect from an HTML iframe. For a work around, see SAC 34259

Smart Devices Applications

In the case of Smart Devices applications, you need to add an event in the login object to authenticate using Facebook.

The logic inside the event associated will include a call to a method of Actions external object, named "LoginExternal".

The first parameter this method receives has to take its value from the Type name defined in the "Authentication Type" definition of the GAM Repository ("Facebook").

Event 'facebook'
    composite
        Actions.LoginExternal("Facebook","","")
        return
    endcomposite
EndEvent

See..

iOS 6.0 Facebook Integration
Windows Phone Facebook Integration

Software Requirements

Java: JDK 1.7 or upper is required to be installed on the application server. Otherwise, the Facebook certificate has to be installed in the key store of the JVM.
Csharp: The certificate of Facebook has to be installed on the windows server.

Notes

1. Facebook Authentication is solved using OAuth.

2. In case you want to "work with friends", or do any particular action after the user has logged in, you need to communicate with the Facebook API. In that case, you'll probably need to get the ExternalToken method of GAMSession EO. The result of invoking this method should be passed to the Facebook API.

3. Facebook API version 2.4 support is available as from GeneXus X Evolution 3 Upgrade 4.

4. For Smart Devices apps, the Actions external object is exclusive of GeneXus 15. For previous versions, you must use SDActions instead.