Amazon RDS for SQL server now supports authentication using the Windows Authentication method. You can now enable your applications to authenticate against Amazon RDS for SQL Server using credentials stored in the AWS Directory Service for Microsoft Active Directory (Enterprise Edition). Keeping all of your credentials in the same directory will save you time and effort because you will no longer have to find and update each copy of the credentials in separate repositories. This may also improve your overall security profile. Windows Authentication support is now available for modern instances as well as existing instances.
Source: amazon.com