Amazon Workspaces uses AWS Directory Services for authentication. If you choose to go with Microsoft AD as a managed Directory Service, you can still integrate this with popular identity providers (like Onelogin, or Okta), allowing you to use the same login and password policies as you have defined in your identity provider.
We typically run workspaces in a private subnet. To reach your private subnet, you can use a VPN Connection (using AWS’s VPN service, or standalone software). When an employee wants to use workspaces, it’ll first need to initiate a VPN connection, then it can use a Workspace client to start the workspace. Once in the Workspace, the employee can use the desktop (Windows or Linux) and access other AWS services that are typically available only through private subnets within the VPC. To make these AWS services available within your VPC, you can use AWS VPC Endpoint interfaces and gateways.