In "Security", you can enable Google G suite or Microsoft office 365 authentication for your workspace members. When enabled, users who sign in with connected G suite or Microsoft office 365 accounts will automatically gain access to the workspace. They will be required to log in with their Google or Microsoft account when accessing the workspace.
If you invite an external user (not a part of your G suite or Microsoft office account) to your workspace, they will not be required to use Single Sign On.
You can also find an invite link you can use to grant access to your workspace. Everyone you share this link with will be able to sign up to your workspace.