Hopefully a quick one: Never implemented OAuth before and the client requires that once the user logs in (using facebook in this case) that this user is tied back to a record our end showing, for examples, which orders they have placed. I'm just trying to figure out the best way to do it.
Can anyone tell me if I can rely on the Facebook User ID from ever changing? Or point me in the direction of a decent article on the subject?
The facebook user Id will always remain constant. To do something similar to what you want you would probably do this:
Step 1 - Authenticate the User
https://developers.facebook.com/docs/authentication/ - You would probably want to use the server side flow.
Step 2 - Get Permissions
https://developers.facebook.com/docs/reference/api/permissions/ - You will need to have the user_about_me permission to get their UserId. You add this to your authentication link above by adding &scope=user_about_me
Please note your redirect_uri must be on the same domain as the settings in your app.
If you wanted to create an enhanced dialog box you can look at this:
https://developers.facebook.com/docs/opengraph/authentication/
Step 3- Getting the userid
If you are doing this inside a Facebook App then look at the userId in the SignedRequest.
Otherwise you use the Graph API. Here a StackOverflow question that shows how: How to get the Facebook user id using the access token
