def call(env)
      case [env['REQUEST_METHOD'], env['PATH_INFO']]
        when ['POST', login_path(env)]; respond(env)
        else @app.call(env)
      end
    end
def call(env)
      case [env['REQUEST_METHOD'], env['PATH_INFO']]
        when ['POST', login_path(env)]; respond(env)
        else @app.call(env)
      end
    end
Instantiates the middleware.

 @param app [Rack app] the Rack application on which this middleware
                       should be layered

 Rack entry point.  Responds to a `POST` to the configured login
 path.

 If the user is authenticated and a URL is given in the `url`
 parameter, then this action will redirect to `url`.

 @param env the Rack environment
 @return a finished Rack response