How to make wordpress cookie authentication?

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C#

REST

Xamarin

authorization

I am using json auth api to authenticate the user.
i am using my wordpress site hosted on 000webhost with https protocol.

When i am logging in i am getting this error message :
System.Net.WebException: The remote server returned an error: (401) Unauthorized

Please i need help,suggestions would be appreciated.

What I have tried:

//On button click

var webRequest = (HttpWebRequest)WebRequest.Create("https://mahdii.000webhostapp.com/users/auth/generate_auth_cookie/?nonce=my_nonce&username=my_username&password=my_password");
            webRequest.Method = "GET";
            webRequest.ContentType = "application/json";
            webRequest.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:28.0) Gecko/20100101 Firefox/28.0";
            webRequest.ContentLength = 0; // added per comment
            string autorization = "username" + ":" + "Password";
            byte[] binaryAuthorization = System.Text.Encoding.UTF8.GetBytes(autorization);
            autorization = Convert.ToBase64String(binaryAuthorization);
            autorization = "Basic " + autorization;
            webRequest.Headers.Add("AUTHORIZATION", autorization);
            var webResponse = (HttpWebResponse)webRequest.GetResponse();
            if (webResponse.StatusCode != HttpStatusCode.OK) Console.WriteLine("{0}", webResponse.Headers);
            using (StreamReader reader = new StreamReader(webResponse.GetResponseStream()))
            {
                string s = reader.ReadToEnd();
                Console.WriteLine(s);
                reader.Close();
            }