SSPI stands for Security Support Provider Interface. The SSPI allows an application to use any of the available security packages on a system without changing the interface to use security services. The SSPI does not establish logon credentials because that is generally a privileged operation handled by the operating system.
Usually a .NETconnection string looks like this, you will have your own server, databse names ofcourse.
“Data Source=localhost\sql2012;Initial Catalog=AdventureWorks;
Other than SSPI you can also use “true”. Integrated Security actually ensures that you are connecting with SQL Server using Windows Authentication, not SQL Authentication; which requires username and password to be provided with the connecting string.