fn intercept(mut req: Request<()>) -> Result<Request<()>, Status> {
    println!("Intercepting request: {req:?}");

    // Set an extension that can be retrieved by `say_hello`
    req.extensions_mut().insert(MyExtension {
        some_piece_of_data: "foo".to_string(),
    });

    Ok(req)
}
This function will get called on each inbound request, if a `Status`
is returned, it will cancel the request and return that status to the
client.
examples/src/interceptor/server.rs