Add "user info http method" setting #32
Description
Currently, in the callback view (OIDCCallbackView), user information is retrieved via a call to pyoidc's get_user_info method.
Unfortunately, it is not possible to specify the type of request (GET or POST) to this method, which poses further problems for pyoidc's do_user_info_request and user_info_request methods.
It would be a good idea to rewrite get_user_info so as to be able to pass the method as a parameter.