IAuthenticationCallbackProvider method names

[PureKrome]

A website needs to implement this interface IAuthenticationCallbackProvider. This allows the developer to handle the callback from the Provider (eg. Google).

eg. Once the user auth's against Google, we come back to our website .. and then what?
i) do we create a new user?
ii) update the details on an existing user?
iii) do we need to ask for more credentials?
iv) did the user reject the permissions request (ie. no Google, don't give out my email).

Ok - so the developer now needs to handle this. Fine.
So i've exposed to interfaces which I believe handle most scenarios.

a) Process
b) OnRedirectToAuthenticationProviderError

Now, with the process .. i'm assuming that MOST of the time the code will be grabbing the user info from the provider and then storing that in the db. Because of this database-assumption I'm wondering

1. if the method Process should be renamed to ProcessAsync and it returns a Task<dynamic>? Assumption here is a db requirement is async. The con to this is that I'm now making assumptions of the developers and it's very possible that they will NOT do any db/I-O bound stuff.
2. For the method OnRedirectToAuthenticationProviderError this is gerenally just a redirect to their own error page. But there is no reason why this method also can't do something I-O bound, like send a logging error to LogEntries or RayGun, etc.

If I leave them as not async, then how would a person do something async in one of those methods if they needed to storea user record asyncly, for example?