Refactor KeycloakClient to use oauth2 and clientcredentials libraries

[fharding1]

Much of the functionality in KeycloakClient for logging in and refreshing the access token seems to re-implement behavior already implemented in golang.org/x/oauth2 and golang.org/x/oauth2/clientcredentials. This issue includes research into whether those libraries would be sufficient, and refactoring KeycloakClient to use them if they are. I would be happy to take this on.

[mrparkers]

I agree, it would probably be better to use an official OAuth2 implementation rather than one implemented in this project.

Feel free to look into this and submit a PR if this is something you're interested in 😄

Thanks for the issue!

[fharding1]

Of course, happy to help out! I actually just submitted a PR to golang/oauth2 that should help out with this (it's still possible to use golang/oauth2 without it but it's a bit more annoying), so I'll see where that goes...

golang/oauth2#396

[mrparkers]

Nice, I like the initiative! I think the PR you submitted has valid use cases even without this provider in mind - hopefully the maintainers agree.