Guard against breaking legacy clients

When the authentication service using angular-resource was introduced
into the client the content type of the app request body for form
submissions was changed from form encoding to json. Therefore, we
should not assume the body is json and deal more appropriately with
legacy clients.
Angular auth -- no need for adding GET params

The usage pattern for the authentication directive is to provide the
authentication service resource as the model. When this is done, the
template binding should take care of ensuring the model is correct,
eliminating the need to copy form values iteratively.