Three domains, three Facebook apps, one authorization?

Question

Facebook

I am doing an Internet project in three languages. It is assumed that each language will have its own domain: for Russian - .ru, for Portuguese - .br, for English - .com. It is also assumed that the .RU and .BR domains will be aliases for .COM, so as not to fence three separate sites, but to process all of them with one engine.
Each site/language will be a Facebook application, generating a feed of news, events and offers within its language to match the audience, speak to it in a language they understand.
I would like:
- so that authorization in the project through Facebook is unified, and not divided into three different applications, that is, that users entering the site are added to one database, regardless of which of the three Facebook applications authorizes them, and not duplicated ;
- so that the user's transition from one language to another (for example, from .RU to .COM, and then to .BR) does not force the user to log in again (that is, does not force the user to give access to his profile to a new Facebook application);
- so that changing the languages ​​of the site does not cause clutter in the user's Facebook feed.
How would you recommend solving the problem?

Answer 1

You need a single entry-exit point (Single Sign-On). You can then use the same Facebook application. Insert the Authorization Iframe into the header of the site.
And google about shared sessions for different domains. If it is PHP, you can transfer authorization data, for example, to MongoDB.