* Adds the `require_token_presence_for_authentication?` DSL option to the Authentication extension which when enabled changes the following behaviour:
1. The `store_in_session` plug will store the user's token rather than their subject in the session.
2. The `retrieve_from_session` plug will look for a stored token in the session rather than a subject and ensure that it's present in the `TokenResource`.
3. The `retrieve_from_bearer` plug will ensure that the token is present in the `TokenResource`.
* Adds the `get_token` action to the `TokenResource`.