Run this Main and open http://localhost:8080/ shows
Hello null!
which means no session. Follow the login and proceed with user:password.
Again visiting the root and confirm the output
Hello MyUserDetailsImpl[…]!
Changing in Main enabling @EnableSpringDataWebSupport.
This will change the order of method argument resolvers and break existing AuthenticationPrincipalArgumentResolver.
Restart the app, repeat the steps and you will see
Hello {}!
indicating there is no null anymore, but something "empty" -- the proxy result.