how to call Microsoft cognitive services face api in unity

FaceApiService.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using Assets.Scripts.Models;
using UnityEngine;

//https://www.packtpub.com/books/content/using-rest-api-unity-part-1-what-rest-and-basic-queries
namespace Assets.Scripts.Services
{
    public class FaceApiService
    {

        private readonly MonoBehaviour _caller;

        private readonly string _queryString =
                "returnFaceId=true&returnFaceLandmarks=false&returnFaceAttributes=age,gender,facialhair,glasses,emotion"; //,

        private string _faceApiUrl;
        private string _results;

        private Dictionary<string, string> _headers;

        public FaceApiResultItemCollection Results
        {
            get
            {
                if (string.IsNullOrEmpty(_results) || _results == "[]")
                {
                    return null;
                }
                FaceApiResultItemCollection resultObject = null;
                try
                {
                    //it's a hack there should be a better way
                    var temp = "{\"FaceApiResultItems\":" + _results + "}";

                    //add objects
                    resultObject = JsonUtility.FromJson<FaceApiResultItemCollection>(temp);
                }
                catch (Exception e)
                {
                    Debug.Log(e.Message);
                }

                return resultObject;
            }
        }



        public FaceApiService(MonoBehaviour caller, string faceApiUrl, string subscriptionKey)
        {
            _faceApiUrl = faceApiUrl;
            if (!string.IsNullOrEmpty(_faceApiUrl) && !_faceApiUrl.EndsWith("/"))
            {
                _faceApiUrl = _faceApiUrl + "/";
            }
            _caller = caller;
            _headers =
                new Dictionary<string, string>
                {
                    {"Ocp-Apim-Subscription-Key", subscriptionKey},
                    {"Content-Type", "application/octet-stream"}
                };

        }


        internal WWW Detect(byte[] imageByteData, Action onCompleteCallback)
        {

            var requesturi = _faceApiUrl + "detect?" + _queryString;
            var www = new WWW(requesturi, imageByteData, _headers);
            _caller.StartCoroutine(WaitForRequest(www, onCompleteCallback));
            return www;
        }

        public WWW Detect(string imageFilePath, Action onCompleteCallback)
        {
            var requesturi = _faceApiUrl + "detect?" + _queryString;
            var byteData = GetImageAsByteArray(imageFilePath);
            var www = new WWW(requesturi, byteData, _headers);
            _caller.StartCoroutine(WaitForRequest(www, onCompleteCallback));
            return www;

        }

        private byte[] GetImageAsByteArray(string imageFilePath)
        {
            var fileStream = new FileStream(imageFilePath, FileMode.Open, FileAccess.Read);
            var binaryReader = new BinaryReader(fileStream);
            return binaryReader.ReadBytes((int)fileStream.Length);
        }

        private IEnumerator WaitForRequest(WWW www, Action onComplete)
        {
            yield return www;
            // check for errors
            if (string.IsNullOrEmpty(www.error))
            {
                _results = www.text;

                if (!string.IsNullOrEmpty(www.error))
                {
                    Debug.Log(_results);
                    Debug.Log(www.error);

                }

                onComplete();
            }
        }
    }
}