public function handle($data)
 {
     $this->validate_request(["assessment", "deadline"]);
     $id = Token::generateNewToken(TOKEN_ASSIGNMENT);
     AssignmentBackend::create_assignment($id, Token::decode($data->{"assessment"}), $data->{"deadline"});
     return ["assignment-id" => $id->toString(), "assessment-id" => $data->{"assessment"}, "deadline" => $data->{"deadline"}];
 }