Get userID in FaceBook from a page inside an iframe app (or replacing )?

Question

Facebook

There is a Facebook page, there is an iframe application on it.
In general, the task of finding out whether the user liked the page or not, I implemented it. There is only one caveat - to get the userID of the user (it is required to check for a like), it is enough to do FB.getUserID(), but only if the user has confirmed that he gives rights to the application (FB.login() is such a popup in which usually it is written what kind of rights, but no rights are requested here).
But this is not an option, because extra step for a simple check.
There used to be a special <fb:visible-to-connection> tag, but now it is deprecated and does not work, and it used to work quite crookedly.
There is another way to get through graph.facebook.com/mebut again, / me needs an access_token, which requires everything the same as the method described above (by the way, on the API page, Facebook substitutes its access_token into the links, and gives what is needed for it, but will it be blocked, as I understand it?).
Can anyone come across?
How to get the ID of the user who is looking at the iframe application from facebook?

Answer 1

Well, sorry, the permission was made specifically for this, so that you just couldn’t get the data until the user allows it. And then it turns out you are trying to bypass the Facebook sandbox.