authZ: more fixes

- fix naming and formatting
- provide more context when erroring auth
- do not capitalize errors
- fix wrong documentation
- remove ugly remoteError{}

Signed-off-by: Antonio Murdaca <runcom@redhat.com>

api/server/middleware.go

@@ -56,6 +56,7 @@ func debugRequestMiddleware(handler httputils.APIFunc) httputils.APIFunc {
 // authorizationMiddleware perform authorization on the request.
 func (s *Server) authorizationMiddleware(handler httputils.APIFunc) httputils.APIFunc {
 	return func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
+		// FIXME: fill when authN gets in
 		// User and UserAuthNMethod are taken from AuthN plugins
 		// Currently tracked in https://github.com/docker/docker/pull/13994
 		user := ""