class Devise::Strategies::Authenticatable

* If all authentication keys are present;
* If the params[scope] returns a hash with credentials;
* If the request hits the sessions controller through POST;
* Validating if the model allows params authentication;

Check if this is strategy is valid for params authentication by:

def valid_for_params_auth?
  params_authenticatable? && valid_params_request? &&
    valid_params? && with_authentication_hash(:params_auth, params_auth_hash)
end