code: func (wfe *WebFrontEndImpl) prepAuthorizationForDisplay(request *http.Request, authz *core.Authorization) {
  	for i := range authz.Challenges {
  		wfe.prepChallengeForDisplay(request, *authz, &authz.Challenges[i])
  		authz.Combinations = append(authz.Combinations, []int{i})
  	}
  	authz.ID = ""
  	authz.RegistrationID = 0
  }
docs: // prepAuthorizationForDisplay takes a core.Authorization and prepares it for
  // display to the client by clearing its ID and RegistrationID fields, and
  // preparing all its challenges.