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

services/vanadium/security/BUILD.gn

Index: services/vanadium/security/BUILD.gn
diff --git a/examples/tiny/BUILD.gn b/services/vanadium/security/BUILD.gn
similarity index 51%
copy from examples/tiny/BUILD.gn
copy to services/vanadium/security/BUILD.gn
index 0a2c73a502ad066b538dedc49ae1bc42de41bc46..53187bd03e10285fb841004628efa19fdb64b58b 100644
--- a/examples/tiny/BUILD.gn
+++ b/services/vanadium/security/BUILD.gn
@@ -2,10 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//mojo/public/mojo_application.gni")
+import("//mojo/go/rules.gni")
 
-mojo_native_application("tiny") {
+go_mojo_application("principal_service") {
   sources = [
-    "tiny.c",
+    "principal_service.go",
+  ]
+  deps = [
+    "//mojo/services/vanadium/security/public/interfaces",
   ]
 }