How to return an error from Tower middleware?

[erikschul]

I'm using the tower example:

I'm trying to:

• intercept request: validate jwt from authorization header, extract claims and embed in extension
• inner.call: grpc handler should perform authorization and save result into extension
• intercept response: check extension for authorization result. if it's missing, return internal server error.

The idea is to ensure that authorization is run on every grpc method.

But how can I return a new Ok(Response) or an Err(...) inside call()?

The types are confusing to me. I think the return is Result<hyper::Response>,tower_service::Service::Error> ?
How do I build each of these types? And what is more correct? new response with status 500, or an Err?
I'd like an example of both if possible.

Thanks!