title: How to get Service Token from Kerberos using SSPI
body: <p><strong>Objective:</strong>
  I am trying to build Proof Of Concept client app to implement Single Sign On by using SSPI. I am new to C# and I am getting confused.</p>
  
  <p><strong>What I know and have done so far:</strong>
  All users are part of Active Directory domain, so I know Kerberos is being used for authentication during login. All I need to do at this point is to get service token from Kerberos so I can pass it to the service resource instead of username and password (correct me if I am wrong). I have been provided Service Principle Name (SPN) and password that has been registered with Kerberos for the service.</p>
  
  <p>I was hoping not to use Platform Invocation Services to call SSPI functions, but I will if I have to. I read through ".NET Remoting Authentication and Authorization Sample - Part I" and used <a href="https://www.nuget.org/packages/Microsoft.Samples.Security.SSPI/" rel="noreferrer">Microsoft.Samples.Security.SSPI</a> for testing. I also tried using <a href="https://github.com/antiduh/nsspi" rel="noreferrer">C#/.Net Interface To The Win32 SSPI Authentication API</a>.</p>
  
  <p>So far, I can get user/client credentials, build client security context. But how do I request a Service Ticket for a given SPN? </p>
  
  <p>I would appreciate your help and guidance. Please be specific if you can and let me know if you have any questions.</p>