A bit of clarification on these -
The User ID Parameter will always be required. This allows us to strongly associate a particular local user with the user identified by the foreign user id.
For the remaining parameters, these are all optional. If they are provided, then these values will be used when creating an account. If the provider is set to update the local database when foreign information changes, these values will also be used to overwrite local values whenever a user logs in. If they are left blank, then on account creation the user should be prompted for these values (just as they would if they were to register using XF's native account system) and the option to update the local database when foreign information changes would become a no-op.
Also, it appears that I cannot update my original post anymore, so I'll say here that I forgot to include a sign out field. When someone logs out of the forum, I expect that this should also trigger a log out of the external provider. Otherwise, you may see issues where the user clicks sign out, then upon navigating to another page or re-opening a link to the forum, they are suddenly signed back in.
