FaceBook user registration in app with several facebook applications
Let’s get started with an example.
There is a company that has several applications and each application has a registration via FaceBook.

If you want to get some information about user — you could do it in such way.

raw_access_token — token that sends front to back.
When we going to each app and making a request to Facebook API it returns:
- for first app:
{ “id”=>”2261241304653674", “email”=> “emma.yeroshek@gmail.com” }
2. for second app:
{ “id”=>”2261239363986091", “email”=>”emma.yeroshek@gmail.com” }
So, each application returns a unique facebook_uid.
What we can do in this case?
First of all, you need to create a company for your application or associate applications with an existing company.
Links below.
Than in your code you can get a list of your applications with unique ids for current user.
In such way.

The example of output:

And you can get ids of user in different facebook apps.

So, now you can resolve it based on the current business logic of the application.
Good luck!
Link that could help you:
https://developers.facebook.com/docs/apps/for-business/
