Authentication.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
using UnityEngine;
using UnityEngine.Networking;

namespace Azure
{
    public class Authentication
    {
        private static Authentication instance;
        static private string Uri = "https://api.cognitive.microsoft.com/sts/v1.0/issueToken";
        public string token;
        private string subscriptionKey;

        private Authentication() { }

        public static Authentication Instance
        {
            get
            {
                if (instance == null)
                {
                    instance = new Authentication();
                }

                return instance;
            }
        }

        public void SetKey(string key)
        {
            this.subscriptionKey = key;
        }

        public IEnumerator AutoFetchToken()
        {
            yield return FetchToken();

            new Timer(new TimerCallback(OnTokenExpiredCallback), this, TimeSpan.FromMinutes(9), TimeSpan.FromMilliseconds(-1));
        }

        private void OnTokenExpiredCallback(object stateIndo)
        {
            FetchToken();
        }

        private IEnumerator FetchToken()
        {
            using (UnityWebRequest www = UnityWebRequest.Post(Uri, "{}"))
            {
                www.SetRequestHeader("Ocp-Apim-Subscription-Key", subscriptionKey);
                yield return www.Send();
                token = www.downloadHandler.text;

                Debug.Log(token);
            }
        }
    }
}

Speech.cs

using System.Collections;
using System.Collections.Generic;
using System.IO;
using UnityEngine;
using UnityEngine.Networking;

namespace Azure
{
    public class Speech
    {
        private static string Uri = "https://speech.platform.bing.com/speech/recognition/interactive/cognitiveservices/v1?language=zh-TW";

        public static IEnumerator interactive(string filePath)
        {
            yield return null;

            using (UnityWebRequest www = UnityWebRequest.Post(Uri, null, File.ReadAllBytes(filePath)))
            {
                www.SetRequestHeader("Authorization", "Bearer " + Azure.Authentication.Instance.token);
                yield return www.Send();
                Debug.Log(www.downloadHandler.text);
            }
        }
    }

}