Setting up third-party server to interact with Game Center

Question

I'm thinking of adding a feature to my iOS game to allow players to create their own game levels, share them with other players, rate them, etc. There'd be a public repository of user-created levels, sortable by creation date, rating, difficulty, or other criteria.

This kind of functionality would necessitate a third-party server. I was thinking I'd create a RESTful API using Sinatra and run it on Heroku. My question is: what would be the best way to authenticate requests to this API? I would prefer not to require players to create a username and password. I'd like to just use Game Center's ID system.

Any suggestions? I've never done any server-side stuff before so any help is appreciated!

Clarification

Yes, I'm aware that Apple doesn't provide its own system. But it does give developers access to unique Game Center identifiers (developer.apple.com/library/mac/#documentation/…) and I was hoping I could use that somehow to roll my own authentication system without requiring users to sign on via Facebook/Twitter/etc. If that's possible.

Answer 1

Looks like as of iOS 7, this is possible with Game Center using:

[localPlayer generateIdentityVerificationSignatureWithCompletionHandler]

Once you have verified the identity of the player using the generateIdentity call,

• Associate the player id with a user on your server's db
• Use whatever access token / authentication pattern your REST framework provides for subsequent calls

https://developer.apple.com/library/ios/documentation/GameKit/Reference/GKLocalPlayer_Ref/Reference/Reference.html

Also for reference, here is the dictionary that we end up sending off to our server based on the response from generateIdentityVerificationSignatureWithCompletionHandler

NSDictionary *paramsDict = @{
    @"publicKeyUrl":[publicKeyUrl absoluteString],
    @"timestamp":[NSString stringWithFormat:@"%llu", timestamp],
    @"signature":[signature base64EncodedStringWithOptions:0],
    @"salt":[salt base64EncodedStringWithOptions:0],
    @"playerID":localPlayer.playerID,
    @"bundleID":[[NSBundle mainBundle] bundleIdentifier]
};