Provide a nicer error message if the user tries to login directly.

Change-Id: I0844fc884a85db8ee6f774c794a143908e754e83
Remove unused parameter, clarify name

Change-Id: I8287e47a665d4734f15804b50514f109d13954cf
Add a missing doc line.
Merge "Provide a nicer error message if the user tries to login directly."