Programmatically determine security context a given SQL Server instance is running under

What is a good way to programmatically determine the security account under which a SQL Server (2005-2014) service is running so that a set of ACLs can be added to a directory allowing it access?

Adding the following links for reference:

http://technet.microsoft.com/en-us/library/ms143504.aspx#Windows

http://technet.microsoft.com/en-us/library/jj219062.aspx

May we all make money in the sequel.