Simple OIDC client to demonstrate authenticating a user's email address.
Currently it only supports Google.
Create a Google OAuth2 application with the OpenID and email scopes and add http://127.0.0.1:5556/ as redirect URI.
Export GOOGLE_CLIENT_ID, GOOGLE_CLIENT_SECRET and run main.go.
This will print a URL and spin up a web server. Visit the URL and consent to sharing your account data and you'll be redirected to the local server, which will parse and validate the redirect and print the email address and subject identifier.