Facebook allowed wildcard domain. So any *.domain.com can be use within single application ID.
Now I want to make every Fan Page will have unique Page Tab URL to my app and the example of URLs one.domain.com, two.domain.com and more.
The subdomain actually point to main app & script will get the subdomain as unique id.
https://developers.facebook.com/docs/appsonfacebook/pagetabs/
I found signed_request can add additional parameter & I’m a bit lost about this one.
May I know the logic how to make sure every Fan Page will have unique URL?
You can only set one Page Tab URL (well two actually, one for HTTP and one for HTTPS).
You can not have different pages use the same app as a page tab and have them access different URLs from the start.
What you can do, is check the page id that you get inside the signed_request parameter – and after that, depending on the page, redirect to wherever you like or output whatever you like.