Hi Alex,
You can use the microflow ‘CustomUserProvisioning’ in user SAML 2.0 module,
Find the below simple microflow to add the User userrole to your SAML authenticated user by default,
For assigning an admin role, if your attribute admin is coming from your AD, then do a REST call by passing this username, fetch the attribute and use exclusive split to assign the admin role as you’re assigning the way user role
Note: In your SAML configuration, check the check box the custom user provisioning settings
Thanks!