Obtaining a Username and Password

Hello,

I'm trying to obtain the username and password the SharePoint site collection admin.  I know this might seem crazy but I have a Nintex workflow and the web service call in the workflow wants authentication.  I've written code to create a credential for this authentication with a hard coded username and password.  I'm wanting to set this with the current username and password of the site collection admin.  How would I go about doing this in Visual Studio 2010?

Thanks in advance,

Shaun