Cache requests to .well-known/openid_configuration/

[amccarthy1]

(related to #18)

Summary

.well-known/openid_configuration/ is a stable resource that is not expected to change between requests. If a caller constructs an AuthClient on every request (which I presume is quite common), then they will hit this endpoint, incurring latency costs and potential for failure. Given the latency on this endpoint, I would imagine these duplicate requests are not cheap to Intuit either.

This redundancy exacerbates issues like #47,

Solution

Currently get_discovery_doc is called each time an AuthClient is constructed, and attached to the Session extended by AuthClient

I would propose instead:

• Do not call get_discovery_doc with a session arg -- it's a static resource that you can access without any auth.
• Annotate get_discovery_doc with @lru_cache (docs) to cache results in-memory for each set of arguments. This is a python builtin.

Happy to contribute a PR for this if interested. I imagine this will provide pretty major cost savings to both Intuit (due to dramatic reduction in duplicate requests) and callers (due to saved compute and less network congestion)

@robert-mings If contributed, would you be open to something like this?