ckeditor5-1.0.x-dev/ckeditor5.routing.yml

ckeditor5.upload_image:
  path: '/ckeditor5/upload-image/{editor}'
  defaults:
    _controller: '\Drupal\ckeditor5\Controller\CKEditor5ImageController::upload'
  methods: [POST]
  requirements:
    _entity_access: 'editor.use'
    _custom_access: '\Drupal\ckeditor5\Controller\CKEditor5ImageController::imageUploadEnabledAccess'
  options:
    parameters:
      editor:
        type: entity:editor

ckeditor5.media_image:
  path: '/ckeditor5/{editor}/is-media-image'
  defaults:
    _controller: '\Drupal\ckeditor5\Controller\CKEditor5MediaController::isMediaImage'
  methods: [GET]
  requirements:
    _entity_access: 'editor.use'
    _custom_access: '\Drupal\ckeditor5\Controller\CKEditor5MediaController::access'
  options:
    parameters:
      editor:
        type: entity:editor