Auth service: Add secret storage\key vault authentication

[nicolehaugen]

This is a stretch goal to try and start attaching to using this functionality more.

Estimate: 4 days

[mjrousos]

What is the scenario here? Is this about storing connection strings/secrets needed by our services (eg. Mongo URL)?

[nicolehaugen]

Adding to last sprint since this was a nice to have - we'll do if we have time. Also, still need clarification on question above.