Initial skeletal implementation of the PrincipalService. Also, use the Login()/GetUserBlessing()

services/vanadium/security/BUILD.gn

+# 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.
+
+import("//mojo/go/rules.gni")
+
+if (defined(go_build_tool) && go_build_tool != "") {
+  go_mojo_application("principal_service") {
+    sources = [
+      "principal_service.go",
+    ]
+    deps = [
+      "//mojo/services/vanadium/security/public/interfaces",
+    ]
+  }
+} else {
+  import("//mojo/public/mojo_application.gni")
+
+  mojo_native_application("principal_service") {
+    sources = [
+      "principal_service.cc",
+    ]
+    deps = [
+      "//base",
+      "//mojo/common",
+      "//mojo/public/cpp/application:standalone",
+      "//mojo/public/cpp/bindings",
+      "//mojo/services/vanadium/security/public/interfaces",
+    ]
+  }
+}