Adding checks for redirect url and tests; fixes #58

[andrewmusselman]

Adding checks and tests for login redirect param.

Rebased on main:

(.venv) $ git fetch origin main
From github.com:apache/infrastructure-asfquart
 * branch            main       -> FETCH_HEAD
(.venv) $ git rebase origin/main
Current branch oauth-redirect-url-58 is up to date.