Hi @naira,
sssd and SSO aren't an either/or in RStudio Workbench, it's a both - and.
RStudio Workbench requires that users exist on the underlying Linux host. In a containerized environment that usually means you'll use sssd to provision users in the container and mount in a persistent volume with home directories. It's also possible to create the users in some other way if you'd prefer not to use sssd.
Configuring SAMLis an additional (optional) configuration to enable an SSO experience for users, but it doesn't affect the user provisioning needs.
More on this here: Authentication in RStudio Pro Products - RStudio :: Solutions
Please feel free to reach out to your RStudio Customer Success rep if you'd like to have a live discussion with an engineer about the options here.