There's some prelimiary work here to pull out the construction of a jinja environment to a separate function.
I wanted to load the template at display time rather than load time, so that it's easy to update on the fly. Honestly, I think we should do this with all our templates: the risk of ending up with malformed templates is far outweighed by the improved turnaround time for an admin trying to update them.
If a user tries to do UI Auth via SSO, but uses the wrong account on the SSO
IdP, try to give them a better error.
Previously, the UIA would claim to be successful, but then the operation in
question would simply fail with "auth fail". Instead, serve up an error page
which explains the failure.
That fallback sets the redirect URL to itself (so it can process the login
token then return gracefully to the client). This would make it pointless to
ask the user for confirmation, since the URL the confirmation page would be
showing wouldn't be the client's.
