How to design a single game account for all platforms?

Question

Game development

Good afternoon!
I am designing the architecture of my game project, which I want to release on iOS, Android, WP and, possibly, further in the social. networks. I came to the conclusion that I can’t figure out how to implement a single game account for all platforms.
More precisely, there is an idea, but it is miserable - to force the user to register, remember his login and password and enter it on all platforms, but this will immediately alienate a large layer of users (for example, children who will forget their data) and, in addition, for this kind of registration you need a password recovery path, for example email, but the reality is that not all users know it (again, hello kids), and linking to a phone number is bad when playing from a social network.
Maybe there are some standard solutions for a similar task?
PS Account is needed to save in-game achievements. This will be an online game.

Answer 1

all conceivable options to support on the server.
normal developed systems support all variants on the server.
and on the client offer or the most suitable for this particular client.
or the person's choice.

Answer 2

oauth via social networks
// EDIT
Then email + password + attachments of social networks accounts