fn default_authority(&self, target: &Url) -> String {
        let path = target.path();
        path.strip_prefix("/").unwrap_or(path).to_string()
    }
Returns the default authority for a channel using this name resolver and
target.  This is typically the same as the service's name.  By default,
the default_authority method automatically returns the path portion of
the target URI, with the leading prefix removed.
grpc/src/client/name_resolution/mod.rs