/// <summary>
        /// Initializes a new instance of the <see cref="T:Xamarin.Cognitive.Speech.SpeechApiClient"/> class.
        /// </summary>
        /// <param name="subscriptionKey">A valid subscription key for the Speech API.</param>
        /// <param name="speechRegion">The <see cref="SpeechRegion"/> where your speech service is deployed.</param>
        /// <param name="authEndpoint">The endpoint used to get the authentication token for the Speech API. Defaults to <see cref="Endpoint.Authentication"/>. To use a custom auth endpoint, set this to an <see cref="Endpoint"/> with your endpoint details.</param>
        /// <param name="speechEndpoint">The endpoint used to talk to the Speech API. Defaults to <see cref="Endpoint.SpeechServiceApi"/>. To use a CRIS/Custom Speech Service endpoint, set this to an <see cref="Endpoint"/> with the details for your CRIS service.</param>
        public SpeechApiClient(string subscriptionKey, SpeechRegion speechRegion, Endpoint authEndpoint = null, Endpoint speechEndpoint = null)
        {
            this.subscriptionKey = subscriptionKey;
            this.authEndpoint    = authEndpoint ?? Endpoints.Authentication;
            this.speechEndpoint  = speechEndpoint ?? Endpoints.SpeechServiceApi;
            this.SpeechRegion    = speechRegion;
            client = new HttpClient();

            AuthClient = new AuthenticationClient(this.authEndpoint, this.subscriptionKey, this.SpeechRegion);
        }