examples: fullstack vweb example (#16761)

examples/vweb_fullstack/src/auth_controllers.v

@@ -0,0 +1,13 @@
+module main
+
+import vweb
+
+['/controller/auth'; post]
+pub fn (mut app App) controller_auth(username string, password string) vweb.Result {
+	response := app.service_auth(username, password) or {
+		app.set_status(400, '')
+		return app.text('error: ${err}')
+	}
+
+	return app.json(response)
+}