Facebook Login is used to enable the following experiences:
Facebook Login lets people quickly and easily create an account in your app without having to set (and likely later forget) a password. This simple and convenient experience leads to higher conversion. Once someone has created an account on one platform, they can log into your app—often with a single click—on all your other platforms. A validated email address means you're able to reach that person to re-engage them at a later date.
Personalized experiences are more engaging and lead to higher retention. Facebook Login lets you access information which would be complex or arduous to collect via your own registration form, for example: the things a person has liked, their birthday, their hometown or current location, their work history. Even just importing someone's profile picture imported from Facebook gives them a stronger sense of connection with your app.
Many highly retentive apps let people connect with their friends in order to enable shared in-app experiences. Facebook Login lets you know which of your app's users are also friends on Facebook so you can build value by connecting people together.
Developers who have implemented Facebook Login in their apps have seen dramatic increases in the number of people logging into their apps, higher levels of engagement, and continuing increases in the number of people using Facebook Login. For details, see Case Studies.
For example, Saavn, a digital music service, experienced 65% higher engagement from people using Facebook Login, 3 times as many shares from people using Facebook Login, and 15 times as many visitors coming from Facebook. Skyscanner, an app for finding flights, hotels, and car rentals, has experienced a 100% increase in the number of people using Facebook Login to access the app.
When people choose to log in with Facebook, they can share their real identity through their public profile. Public Profile includes a person's real name, a profile picture, their gender and their locale. Apps based on real identity often have less spam and foster higher quality conversations.
Cross Platform Login
Facebook Login is available on the most common mobile and desktop app platforms. People who create accounts with Facebook on one platform can quickly and easily log into your app on another. A person is known by the same User ID everywhere so they can pickup your in-app experience where they left off. Facebook Login is available on iOS, Android, Web, and Windows Phone, for desktop apps and for devices such as Smart TVs and Internet of Things objects
Works Alongside Your Existing Account System
Facebook Login complements your existing account system. Give people the option to log in with Facebook alongside email, SMS or other social login choices. Where an email address you get from Facebook Login matches one already in your system, you can log that person into their existing account without additional passwords.
Facebook Login supports over 30 permissions which determine which information people share with your app. This means you have precise control over what you request and people have precise control over what they choose to approve.
People Have Control Over What They Share
Great experiences start by giving people control. With Facebook Login, people can choose which information they share with your app. They can still get the benefits of logging in with Facebook even if they feel uncomfortable granting access to certain information. Your app can later re-request this information once you've explained how the person's experience will be enhanced.
Facebook Login supports the gradual authorization—you don't have to request all the information you want up front—you can do it over time. This means people can quickly and easily create accounts in your app—and as their experience with your app deepens, you can request addition information to further enhance their experience.
We want to ensure the tens of millions of people who use Facebook Login every day have a safe, reliable and consistent experience. Login Review helps determine if apps that are requesting access to detailed account information have built great experiences.
Our Login Review process is designed to be fast and lightweight. Our review team actually use your app and will provide guidance and feedback to ensure you're meeting our Platform Policies.
Apps may ask for the following three permissions from any person without submitting for review by Facebook:
To ask for any other permission, your app will need to be reviewed by Facebook before these permission become visible in the Login Dialog to the public who're logging into your app with Facebook.
However, to help you develop your Facebook Login experience, anyone listed in the Roles section of your app's dashboard will be able to grant any valid permission without approval from Facebook.
Learn more about Login Review.
How to get the most out of Facebook Login and Graph API v2.x
From F8 2015, Simon Cross and Chris Lang talk through improvements to stability, new iOS and Android SDKs and how to handle declined permissions.