My game, Carnage in Space II, has a custom login system that lets players (optionally) sign in, automatically sync their save files between computers, and view highscores and achievements all on my website regardless of where it's being played from. Currently, you can play the game from my website (http://carnageinspace.com) or Newgrounds; I plan to add Chrome Store and Kongregate.
The problem is, Kongregate doesn't want any games to have login systems outside of their own.
What I'd like is to have the game check if you're on Kongregate, and then send you to the custom login or the Kongregate login. I can customize my website to allow Kongregate accounts alongside normal ones, storing their Kongregate name instead of an email address.
My problem: I don't see a way to detect that the game is Kongregate. How do I do that?