Third-party developers can make use of Facebook's new anonymous login feature as well as an improved Facebook Login feature to provide users with options to log in to their apps or services using Facebook accounts.
Anonymous Login has been designed to provide Facebook users with an option to try out an application or service without sharing information with it.
Apps may request information about a Facebook user when the Facebook account is used to create an account. The idea behind the new login option is to give users an option to test an app or service before they decide if they want to fully commit to it.
An anonymous trial so to speak. It works similar to the regular log in with Facebook but with the difference that personal information are not shared if the option is selected.
This means that the app developer won't receive data from the associated account while everything remains the same for Facebook in this regard (the company still knows which apps you use anonymously).
The log in anonymously option is displayed on the sign up or log in page of applications supporting the feature. If the anonymous login option is selected, no Facebook information will be shared with the app.
Users can switch to the regular Facebook Login at any time later on, for instance if they want to make use of features that require account information (such as pushing updates to Facebook).
Facebook notes that the feature is tested with a few developers currently and that additional developers will be invited to it in the coming months.
It should be clear that you stay only anonymous from the app developers but not Facebook if you use that feature. It should come in handy for Facebook users who test new applications regularly or even only occasionally, especially if they don't want to share any personal information with apps that they run using their Facebook account.
Facebook announced better controls for its regular Facebook Login authentication system. With the new Facebook Login system, users can edit the information that they provide to third-party applications and services.
To make use of that, you have to click on the "edit the info you provide" link during login. Here you can disable access to personal information that are not required.
As you can see on the screenshot above, the public profile information is a required field, while everything else including the email address, birthday and likes are not.
The new login will roll out over the course of the next few months.
I believe that this solves an issue that app developers have faced who implemented Facebook authentication into their apps. Part of the overall userbase on Facebook does not want to share information with third-party apps. While this is especially true on first run, some may not want to share information at all with an app, and the new anonymous login feature provides them with an option to block information sharing without having to give up on the application.