Actually, developers are only forced to implement it _if_ they support logging in with other social auths.
A big problem of many apps is that they only had a "log in with google"/"log in with facebook" button, which is very problematic for people who have neither.
On Android this is more acceptable since you need a Google account for the OS itself anyway.
A big problem of many apps is that they only had a "log in with google"/"log in with facebook" button, which is very problematic for people who have neither.
On Android this is more acceptable since you need a Google account for the OS itself anyway.