Add auth flow debug logging

[LucaButBoring]

Is your feature request related to a problem? Please describe.
Debugging auth flows is a frustrating experience, since there are many cases where the client SDK will handle a request failure or parsing issue by silently falling back to other behaviors. Having debug logging in the auth flow would make it significantly easier to see what's going on when steps fail.

Describe the solution you'd like
It'd be great if we could use debug or something similar to get debug logging at least on every major step and error.

Describe alternatives you've considered
The status quo - manually adding logging statements to the SDK to debug, or monitoring server requests and reverse-engineering the behavior from there.

Additional context
Some examples of where this would be very useful:

• Discovering protected resource metadata (error gets silently thrown out here)
• During token refreshes (errors silently thrown out here)
• During resource metadata URL parsing here