Auth route /whoami for nginx subrequest auth, support changing the session cookie domain for that purpose

lib/sso_bsn_web/controllers/user_session_controller.ex

@@ -23,4 +23,13 @@ defmodule SsoBsnWeb.UserSessionController do
     |> put_flash(:info, "Logged out successfully.")
     |> UserAuth.log_out_user()
   end
+
+  def check_auth(conn, _params) do
+    user = conn.assigns[:current_user]
+    conn
+    |> put_resp_header("X-Auth-Username", user.username)
+    |> json(%{
+      username: user.username
+    })
+  end
 end