Replace pyjwkest

[jmbowman]

The pyjwkest package was abandoned upstream more than 3 years ago. Let's replace it with something more actively maintained. First check to see if the latest version of PyJWT (already used here) supports what we need from pyjwkest. If not, I nominate Authlib as seeming to cover the same functionality with much more usage and active maintenance, but feel free to do a quick search on PyPI or elsewhere for a better replacement.

[jmbowman]

Maybe jpadilla/pyjwt#723 added what we need? Not sure without further digging into how this works.