Lsass.exe is the Local Security Authentication Server. It verifies the validity of user logons to your PC or server.
Lsass generates the process responsible for authenticating users for the Winlogon service.
This is performed by using authentication packages such as the default, Msgina.dll. If authentication is successful,
Lsass generates the user's access token, which is used to launch the initial shell. Other processes that the user initiates then inherit this token.