code: func (ra *RegistrationAuthorityImpl) authzValidChallengeEnabled(authz *core.Authorization) bool {
  	for _, chall := range authz.Challenges {
  		if chall.Status == core.StatusValid {
  			return ra.PA.ChallengeTypeEnabled(chall.Type)
  		}
  	}
  	return false
  }
docs: // authzValidChallengeEnabled checks whether the valid challenge in an authorization uses a type
  // which is still enabled for given regID