crossword-8.x-1.x-dev/modules/crossword_contest/crossword_contest.routing.yml

crossword.contest:
  path: '/crossword-contest/{mid}/{answer}'
  defaults:
    _controller: 'Drupal\crossword_contest\Controller\CrosswordContestController::build'
  requirements:
    _permission: 'view media'
    _custom_access: 'Drupal\crossword_contest\Controller\CrosswordContestController::validateMid'
    mid: \d+