I have one .net desktop application that first ask for the salesforce username and password to login and once log-in success, it will fetch some data from the org (using Salesforce API).
Now, my customer has implemented SSO with Active Directory in his salesforce Org and he also want to implement same in .net application. 
So, I want to implement SSO in .net application so that user doest not need to remember credentials and can be authenticated by Windows Login.
Anyone have idea how I can implement this in .net Application? Any example available for implementing SSO in .net desktop application?

Using Apex in a trigger, how can one find the current SFDC instance (the pod - like "cs3") when in a sandbox logged in under a My Domain?  Using Url.getSalesforceBaseUrl().getHost(); doesn't seem to get us there.