A custom controller should return content based on parameters:

• hidden: shows hidden content if set to 1, hide otherwise
  /api/ezp/v2/ez_recommendation/v1/content/ {contentId}?hidden=1
  should display content even if it's hidden
  
  
  /api/ezp/v2/ez_recommendation/v1/content/{contentId}

  ?hidden=0
  should return 204 No Content

• path: return content from specified subtree
  /api/ezp/v2/ez_recommendation/v1/contenttypes/ {contentTypeId}

  ?path=/1/2/