What's the best way to handle SSO, SCIM, and RBAC together in a SaaS app?

The best way is to treat them as three layers of the same identity system rather than separate features:

1. SSO = authentication

   • Proves who the user is.
   • Commonly via SAML or OIDC.
   • Should create or link a user in your app, but not directly grant app permissions beyond a basic default.

2. SCIM = provisioning and lifecycle

   • Creates, updates, deactivates users and groups from the customer’s IdP.
   • Use it to keep your app’s user directory in sync.
   • Let SCIM manage:
     • user creation
     • name/email updates
     • deactivate/reactivate
     • group membership
     • optional role assignment mappings

3. RBAC = authorization

   • Determines what the user can do inside your app.
   • Should be enforced from your app’s internal permission model, not directly from the IdP.
   • Use roles as a stable abstraction:
     • org_admin
     • billing_admin
     • member
     • read_only
   • Map IdP groups or SCIM groups to these roles where appropriate.

Recommended architecture

1) Maintain an internal identity model

Have internal objects like:

• Organization / Tenant
• User
• Group
• Role
• Membership
• ExternalIdentity (IdP subject / SCIM identifier)

This gives you a durable app-side source of truth for authorization.

2) Separate authentication from authorization

• On SSO login, verify the assertion/token.
• Resolve the user to an internal account.
• Then load roles/permissions from your database.
• Do not trust SSO alone for fine-grained access.

3) Use SCIM for account and group sync

SCIM should be the primary way enterprise customers manage:

• user onboarding/offboarding
• group assignment
• sometimes default roles

If SCIM says a user is deprovisioned, immediately disable access, even if they can still technically authenticate.

4) Map groups to roles

A common pattern:

• IdP group Finance-Team → app role billing_admin
• IdP group All-Employees → app role member

Keep the mapping:

• explicit
• tenant-specific
• editable by admins
• auditable

Avoid hardcoding assumptions across customers.

5) Prefer role templates over direct permission assignment

If you let SCIM assign permissions directly, things get messy. Better:

• SCIM syncs group membership
• groups map to roles
• roles map to permissions

This keeps your system understandable and portable.

Practical rules that help

• SSO should not create privilege by itself
  • At most, it should auto-provision a user into a default role.
• SCIM should be authoritative for existence and group membership
  • If SCIM disables a user, access is revoked.
• RBAC should be authoritative for app behavior
  • Even if a user is authenticated, every protected action checks roles/permissions.
• Support multiple identity sources
  • Some customers will use SSO only.
  • Some will use SSO + SCIM.
  • Some may want local admins too.

Good onboarding flow

1. Customer configures SSO.
2. Customer configures SCIM.
3. First SCIM push creates users/groups.
4. First login via SSO links the identity.
5. Admin maps groups to roles.
6. App enforces permissions based on internal RBAC.

Common pitfalls

• Using the IdP group name as the app’s permission model directly
• Letting SSO create users without a tenant boundary
• Not handling deprovisioning immediately
• Mixing “who the user is” with “what the user can do”
• No audit trail for group/role changes
• Assuming email is a stable identifier
• Not supporting just-in-time provisioning fallback when SCIM isn’t enabled

Best practice in one sentence

Use SSO to authenticate users, SCIM to provision and sync identities/groups, and RBAC inside your app to authorize actions, with a tenant-scoped mapping between external groups and internal roles.

If you want, I can also sketch a reference data model or request/auth flow diagram for this setup.