Add support for OAuth2 authentication

[travishathaway]

What is the idea?

Improve the existing implementation for OAuth2.

Why is this needed?

The current implementation relies on a copy and paste approach to token handling (not ideal) and has no test coverage. Furthermore, it needs to be tested against a real OAuth2 provider to make sure that we can support this type of workflow.

What should happen?

• Explore using a local server approach to handle saving and using the authorization token in conda
• Add test coverage (focus on unit testing with mocks; not integration testing)
• Add better error handling to make it obvious to the user that the channel authentication is not working; make sure the error messages point to how they could fix it.

[travishathaway]

Potentially helpful:

• https://github.com/aovasylenko/keycloak-auth-demo/tree/main