auth.js

function auth(component) {

    return {
        controller: function () {
            var ctrl = this;
            function success(user) {
                Account.user(user)
                ctrl.output = new component.controller()

                m.redraw(true)
            }

            function failure(err) {
                m.route('/login')
            }

            if (!Account.user()) {
                Account.identity().then(success, failure)
            } else {
                success(Account.user())
            }
            
        },

        view: function (ctrl) {
            return ctrl.output
              ? component.view(ctrl.output)
              : { subtree: 'retain' }
        }
    }
}

Mithril authorisation with component logic