func getAuth(clientId string, accessToken string, http *http.Request) *hawk.Auth {
	// Create the hawk authentication string from the request...
	credentials := &hawk.Credentials{
		ID:   clientId,
		Key:  accessToken,
		Hash: sha256.New,
	}
	return hawk.NewRequestAuth(http, credentials, 0)
}
// SignRequest will add an Authorization header
func (c *Credentials) SignRequest(req *http.Request) (err error) {
	// s, err := c.SignHeader(req.Method, req.URL.String(), hash)
	// req.Header.Set("Authorization", s)
	// return err

	credentials := &hawk.Credentials{
		ID:   c.ClientID,
		Key:  c.AccessToken,
		Hash: sha256.New,
	}
	reqAuth := hawk.NewRequestAuth(req, credentials, 0)
	reqAuth.Ext, err = getExtHeader(c)
	if err != nil {
		return fmt.Errorf("Internal error: was not able to generate hawk ext header from provided credentials:\n%s\n%s", c, err)
	}
	req.Header.Set("Authorization", reqAuth.RequestHeader())
	return nil
}
// apiCall is the generic REST API calling method which performs all REST API
// calls for this library.  Each auto-generated REST API method simply is a
// wrapper around this method, calling it with specific specific arguments.
func (awsProvisioner *AwsProvisioner) apiCall(payload interface{}, method, route string, result interface{}) (interface{}, *CallSummary) {
	callSummary := new(CallSummary)
	callSummary.HttpRequestObject = payload
	var jsonPayload []byte
	jsonPayload, callSummary.Error = json.Marshal(payload)
	if callSummary.Error != nil {
		return result, callSummary
	}
	callSummary.HttpRequestBody = string(jsonPayload)

	httpClient := &http.Client{}

	// function to perform http request - we call this using backoff library to
	// have exponential backoff in case of intermittent failures (e.g. network
	// blips or HTTP 5xx errors)
	httpCall := func() (*http.Response, error, error) {
		var ioReader io.Reader = nil
		if reflect.ValueOf(payload).IsValid() && !reflect.ValueOf(payload).IsNil() {
			ioReader = bytes.NewReader(jsonPayload)
		}
		httpRequest, err := http.NewRequest(method, awsProvisioner.BaseURL+route, ioReader)
		if err != nil {
			return nil, nil, fmt.Errorf("apiCall url cannot be parsed: '%v', is your BaseURL (%v) set correctly?\n%v\n", awsProvisioner.BaseURL+route, awsProvisioner.BaseURL, err)
		}
		httpRequest.Header.Set("Content-Type", "application/json")
		callSummary.HttpRequest = httpRequest
		// Refresh Authorization header with each call...
		// Only authenticate if client library user wishes to.
		if awsProvisioner.Authenticate {
			credentials := &hawk.Credentials{
				ID:   awsProvisioner.ClientId,
				Key:  awsProvisioner.AccessToken,
				Hash: sha256.New,
			}
			reqAuth := hawk.NewRequestAuth(httpRequest, credentials, 0)
			if awsProvisioner.Certificate != "" {
				reqAuth.Ext = base64.StdEncoding.EncodeToString([]byte("{\"certificate\":" + awsProvisioner.Certificate + "}"))
			}
			httpRequest.Header.Set("Authorization", reqAuth.RequestHeader())
		}
		debug("Making http request: %v", httpRequest)
		resp, err := httpClient.Do(httpRequest)
		return resp, err, nil
	}

	// Make HTTP API calls using an exponential backoff algorithm...
	callSummary.HttpResponse, callSummary.Attempts, callSummary.Error = httpbackoff.Retry(httpCall)

	if callSummary.Error != nil {
		return result, callSummary
	}

	// now read response into memory, so that we can return the body
	var body []byte
	body, callSummary.Error = ioutil.ReadAll(callSummary.HttpResponse.Body)

	if callSummary.Error != nil {
		return result, callSummary
	}

	callSummary.HttpResponseBody = string(body)

	// if result is passed in as nil, it means the API defines no response body
	// json
	if reflect.ValueOf(result).IsValid() && !reflect.ValueOf(result).IsNil() {
		callSummary.Error = json.Unmarshal([]byte(callSummary.HttpResponseBody), &result)
		if callSummary.Error != nil {
			// technically not needed since returned outside if, but more comprehensible
			return result, callSummary
		}
	}

	// Return result and callSummary
	return result, callSummary
}