support docker registry 2.8.x version which not support auto redirect path (#397)

Author: docooler

auth_server/server/server.go

@@ -436,6 +436,8 @@ func (as *AuthServer) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		as.doIndex(rw, req)
 	case req.URL.Path == path_prefix+"/auth":
 		as.doAuth(rw, req)
+	case req.URL.Path == path_prefix+"/auth/token":
+		as.doAuth(rw, req) 
 	case req.URL.Path == path_prefix+"/google_auth" && as.ga != nil:
 		as.ga.DoGoogleAuth(rw, req)
 	case req.URL.Path == path_prefix+"/github_auth" && as.gha != nil: