Within QGIS when you set up a connection to a MS SQL Server instance you are presented with two options. Here’s a bit of clarification on what the two options entail.
* Trusted connection – this is the same thing as using Windows Authentication and authentication is managed by the domain and authorization is handled by SQL Server – This could be handled by an Active Directory Security Group.
* Login – SQL Server can also use its own logins such as a user. These are both authenticated and authorized by SQL Server. They are only viable if SQL Server is configured to run in Mixed Authentication mode.