It seems handle_errors doesn't work at all in caddy when forward_auth is used
this means the examples in the the readme are wrong.
You should check in the caddy documentation using the get-library-docs tool if forward_auth responses could be processed or will caddy always reply with a 401 no matter what.
Agents.md gives a general overview of the project.
Use the integration test environment under the dev directory to test this out using docker.
if using handle is possible with forward_auth, then update the readme with accurate examples
if not remove any examples using handle_error and other handle directives.