Google is working on making it easier to sign in into your games (Android, Play Games On PC, Chromebook etc) by integrating a recall API in Play Games Services (PGS). This is possible with the latest update to the play-services-games-v2 library. Developer can integrate it in their game clients using Java SDK and Unity SDK. Google Play Services is also updated by Google to support this feature and mentioned in their GMS changelog.

If you have ever installed Google Play Games from Play Store, you may be aware that it lets you create a profile and you can use that profile to sign in into your games. This profile is unique and have a username and connected to your Google account. The whole point of this thing is to make it easier to sign into game and track your progress. 

But consider a scenario, like you have an account in PubG and you created that account using your email and password. Also you have a Google Games profile with a username but that's not connected to your game login credentials in any way. You have to enter your email and password every time you install that game or install it on your other devices such as your tablet or chromebook. With Recall API, Google is eliminating the need of entering email and passwords every time you do this thing.  

With Recall API, the game can link your game server credentials (email and passwords) to your Google games profile. By doing that, the game can directly request your Google games profile username and check if the username is linked to any game server credentials (email and password). If it find any linked profile to game server credentials, you will be logged in directly without entering email and passwords. 

There are various other things related to it such as Cardinality rules and encryption, you can read about all of them here. Google did a great job on explaining this thing easily as well on that page. 

Source : Recall API