Reconcile MakeAuthOptions and PopulateAuthOptions

These functions are used in separate places and appear to have similar intent, but while PopulateAuthOptions preserves the existing options its given, MakeAuthOptions discards them. This seems incorrect on the surface, but there may be reasons why it behaves this way. Further investigation is needed to determine if MakeAuthOptions can be changed to preserve the options passed in and/or the two functions could be merged.

Locate MakeAuthOptions and PopulateAuthOptions, then compare how each handles the options it receives and where each function is used. Determine whether preserving existing options is safe and whether the functions can be merged; done means documenting the behavior decision and validating the affected authentication paths.

Written by the indexing model from the issue text.