Question

I have a webapp on google app engine that checks to see if a user is logged in (through the federated id) with the following code. I just changed domain names and now for some reason it isn’t recognizing any of my current users. This is because the openID changes depending on the domain name which I found through a little testing. Is there any workaround or way to let these users log in?

user = users.get_current_user()
currentregistereduser = None
try:
    user_db_qry = User.query(User.theid == user.federated_identity())
    user_db_list = user_db_qry.fetch(1)
    currentregistereduser = user_db_list[0]

    # I go on here to do all of the stuff for a logged in user

#if the user does not exist yet
except IndexError:
    logging.error("indexerror" + str(User.theid) + " and " + str(user.federated_identity()))
    user_db = User(
        name=user.nickname(),
        email=user.email(),
        theid=user.federated_identity(),
        visits = 0,
        medals = 0,
        prestige = 1,
        )
    user_db.put()
    #they go on to create their profile data here
    self.redirect("/profile")

Answer 1

This seems to be a similar problem to the one faced by StackExchange when it implemented OpenID. You can see how they dealt with it here:
https://blog.stackoverflow.com/2010/04/openid-one-year-later/

From that page:

So our cross-site user account matching now works this way:

1. Match by GUID. This is something we generate and assign during account association, so it’s a perfect fingerprint.

2. match by OpenID URL. This works for the vast majority of OpenID providers.

3. match by OpenID provided email address … if you are on our trust whitelist. This works for those rare OpenID providers (currently, only Google GMail) who generate domain-specific identifiers.

You could also try using a OpenID Library. Several are listed here:
http://openid.net/developers/libraries/

Hope this helps.