Add one more redirect to finalize login on the GSS slave

This patch will move final login steps back to slave so we can use all login related events on the slave, mostly to enable mfa logins.

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I think that addressed all of the feedback?

@ArtificialOwl what is the status of this? Both the stepupauth[0] app and mfazones[1] app are nearing completion, but will not work with gss without this patchset.

0. https://apps.nextcloud.com/apps/stepupauth
1. https://apps.nextcloud.com/apps/mfazones1