Added tip to enable CsrfTokenManager as service

in the framework configuration file as it is required for autowiring on the ExampleFormAuthenticator constructor

Author: jonasarts

security/guard_authentication.rst

@@ -519,6 +519,11 @@ service to be passed) and add the following logic::
 
         // ...
     }
+    
+.. tip::
+
+    Don't forget to enable `csrf_protection` in the `config/framework.yml` file that 
+    CsrfTokenManagerInterface can get autowired.
 
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