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

examples/echo/echo_client.cc

Index: examples/echo/echo_client.cc
diff --git a/examples/echo/echo_client.cc b/examples/echo/echo_client.cc
index 28ba874a2a17579f77c084b24e527a5f236e3b56..d03024a43e8337ae95faefa82c5e9bb7661bdb31 100644
--- a/examples/echo/echo_client.cc
+++ b/examples/echo/echo_client.cc
@@ -10,6 +10,7 @@
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/public/cpp/application/application_runner.h"
 #include "mojo/public/cpp/utility/run_loop.h"
+#include "mojo/services/vanadium/security/public/interfaces/principal.mojom.h"
 
 namespace mojo {
 namespace examples {
@@ -26,13 +27,21 @@ class ResponsePrinter {
 class EchoClientDelegate : public ApplicationDelegate {
  public:
   void Initialize(ApplicationImpl* app) override {
-    app->ConnectToService("mojo:echo_server", &echo_);
+    // Get user login credentials
+    app->ConnectToService("mojo:go_principal_service", &login_service_);
+    login_service_->Login(Callback<void(const BlessingPtr)>());
 
+    app->ConnectToService("mojo:echo_server", &echo_);
     echo_->EchoString("hello world", ResponsePrinter());
   }
 
+  void Quit() override {
+    login_service_->Logout();
+  }
+
  private:
   EchoPtr echo_;
+  PrincipalServicePtr login_service_;
 };
 
 }  // namespace examples