code: func (ch *CredHub) InterpolateString(vcapServicesBody string) (string, error) {
  	if !strings.Contains(vcapServicesBody, `"credhub-ref"`) {
  		return vcapServicesBody, nil
  	}
  
  	requestBody := map[string]interface{}{}
  	if err := json.Unmarshal([]byte(vcapServicesBody), &requestBody); err != nil {
  		return "", err
  	}
  
  	resp, err := ch.Request(http.MethodPost, "/api/v1/interpolate", nil, requestBody, true)
  	if err != nil {
  		return "", err
  	}
  
  	defer resp.Body.Close()
  
  	if err := ch.checkForServerError(resp); err != nil {
  		return "", err
  	}
  
  	body, err := ioutil.ReadAll(resp.Body)
  	if err != nil {
  		return "", err
  	}
  
  	return string(body), nil
  }
docs: //InterpolateString translates credhub refs in a VCAP_SERVICES object into actual credentials