How to Encode the username and Pwd to NTLM authentication

Oct 22 2018 7:39 AM
string username = AHD.username;
string password = AHD.password;
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(username + ":" + password);
string encodedCredentials = System.Convert.ToBase64String(plainTextBytes);
string authorization = String.Concat("SDM", encodedCredentials);
The above code i am using for SDM encoded credentials but i am getting the basic authentication. 
In the way i need NTLM authentiction values as i am getting the values in postman but not in coding. what approch is used to get NTLM as like Basic authentication

Brought to you by: