Add User service.

service/user/user.go

Index: service/user/user.go
diff --git a/service/user/user.go b/service/user/user.go
new file mode 100644
index 0000000000000000000000000000000000000000..f8e1c55633b52cae7e62224b667db7b9eb3829ee
--- /dev/null
+++ b/service/user/user.go
@@ -0,0 +1,23 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package user
+
+import "google.golang.org/appengine/user"
+
+// User is a mimic of https://godoc.org/google.golang.org/appengine/user#User
+//
+// It's provided here for convenience, and is compile-time checked to be
+// identical.
+type User struct {
+	Email             string
+	AuthDomain        string
+	Admin             bool
+	ID                string
+	ClientID          string
+	FederatedIdentity string
+	FederatedProvider string
+}
+
+var _ User = (User)(user.User{})

[Vadim Sh., 2015/12/03 00:55:56]

o_O didn't know it works that way

[iannucci, 2015/12/03 01:00:24]

All public fields with matching names and types == castable.

https://www.youtube.com/watch?v=m1wKxHQmBAg