Single Signon from company website

I am trying to implement single signon per website user for our front end app so users don't have to log in the website twice.

I tried to use below code from Prologika site, however it fails on web request and I constantly get 400 - Bad Request error.

I have checked userid, password, client id etc. and everything is correct.  I have also tried UI based three-leg auth and that works fine.

Please let me know, if you have an idea or alternate to do this.  My company can pay for a license per user but does not want them to login twice.  We want users to be agnostic of Power BI log in.

Snippet

// perform two-leg OAuth                  System.Net.WebRequest request = System.Net.WebRequest.Create("https://login.microsoftonline.com/e7b81d0a-a949-4103-83dc-feff6277c109/oauth2/token") as System.Net.HttpWebRequest;                  request.ContentType = "application/x-www-form-urlencoded";                  request.Method = WebRequestMethods.Http.Post;                  using (StreamWriter streamWriter = new StreamWriter(request.GetRequestStream()))                  {                      string payload = String.Format("grant_type=password&client_id={0}&client_secret={1}&resource=https%3a%2f%2fanalysis.windows.net%2fpowerbi%2fapi&username={2}&password={3}",                           WebUtility.UrlEncode(Properties.Settings.Default.ClientID), WebUtility.UrlEncode(Properties.Settings.Default.ClientSecret),                          WebUtility.UrlEncode(powerBIUserID), WebUtility.UrlEncode(Util.ToInsecureString(powerBIPassword)));                      streamWriter.Write(payload);                  }                  using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())                  {                      using (StreamReader streamReader = new StreamReader(response.GetResponseStream()))                      {                          string payload = streamReader.ReadToEnd();                          payload = payload.Replace("access_token", "AccessToken");                          payload = payload.Replace("refresh_token", "RefreshToken");                          AuthenticationResult ar = AuthenticationResult.Deserialize(payload);                          Session["authResult"] = ar;                      }                  }

Thanks in advance.