I'm building a multi-tenant product and need SSO, provisioning, and role-based access. Where should I start?

A good place to start is to separate the problem into three layers:

1. Authentication — “Who is the user?”
2. Provisioning / lifecycle — “How does the user get created, updated, disabled?”
3. Authorization — “What can the user do once inside?”

For a multi-tenant SaaS, I’d recommend this path:

1) Define your identity model first

Before choosing tools, decide how identities map to your product.

Key questions:

• Is a user global across all tenants, or does each tenant have its own user record?
• Can one person belong to multiple tenants?
• Do you need tenant-level admins and product-level admins?
• Do roles differ by tenant, by app module, or by resource?

A common model:

• User = person
• Tenant/Organization = customer account
• Membership = user’s relationship to a tenant
• Role = assigned on the membership, not directly on the user
• Permissions = what the role can do

This avoids headaches later.

2) Pick your SSO standard: start with SAML or OIDC

If you’re selling B2B, you’ll likely need support for:

• SAML 2.0 for enterprise SSO
• OIDC / OAuth 2.0 for newer IdPs and simpler integrations

My suggestion:

• Support OIDC first if you can — it’s easier to implement and debug.
• Add SAML if your customers require it, which many enterprise buyers still do.

Important features:

• SP-initiated and IdP-initiated login
• Domain-based IdP discovery
• Just-in-time account creation
• Tenant-specific IdP configuration

3) Plan provisioning with SCIM

For enterprise customers, provisioning usually means SCIM 2.0.

SCIM lets the customer’s IdP or directory:

• create users
• update user attributes
• deactivate users
• manage group membership

For multi-tenant SaaS, SCIM should map to:

• tenant
• membership
• role/group assignment

Start by supporting these SCIM objects:

• User create/update/deactivate
• Optional group sync
• Attribute mapping like email, name, externalId, department

If you need an MVP, you can begin with:

• SSO + JIT provisioning
• then add SCIM later

But if enterprise sales is the goal, SCIM is often expected.

4) Build RBAC cleanly

For authorization, start with RBAC rather than jumping into complex policy engines.

Recommended structure:

• Tenant-level roles: Owner, Admin, Member, Viewer
• System roles: Support, Internal Admin, Billing Admin
• Optional resource roles later

Best practice:

• Keep roles small and understandable
• Map roles to permissions explicitly
• Use middleware/guards in your app, not just UI checks
• Log authorization decisions for auditability

If your app will become very complex, you can later evolve into:

• RBAC + ABAC
• or a policy engine like OPA, Cedar, or similar

5) Decide build vs buy

For most teams, identity is not the best place to reinvent everything.

Buy if:

• you want to launch fast
• enterprise SSO/SCIM is a requirement
• you don’t want to maintain edge cases around IdPs, certificates, SCIM, and audit logs

Build if:

• you have strong security/infra expertise
• the requirements are unusually custom
• identity is core to your product differentiation

Common options:

• Auth0 / Okta / WorkOS / Clerk / FusionAuth / Azure AD B2C / Cognito
• For enterprise SSO + SCIM specifically, WorkOS is often used as a shortcut
• For more control and lower cost at scale, Auth0/FusionAuth/Cognito are common choices depending on your stack and constraints

6) Start with these MVP milestones

A practical sequence:

Phase 1

• Email/password or social login (if needed)
• Tenant creation
• Membership model
• Basic RBAC

Phase 2

• OIDC SSO
• Tenant-specific IdP config
• Domain-based login routing

Phase 3

• SAML support
• JIT provisioning
• Audit logs

Phase 4

• SCIM provisioning
• Group-to-role mapping
• Deprovisioning / disable flows
• Fine-grained authorization if needed

7) Security essentials you should not skip

• Enforce MFA for admins if possible
• Encrypt secrets/certificates at rest
• Support certificate rotation for SAML
• Use short-lived sessions and refresh tokens carefully
• Separate tenant data strictly at the data layer
• Add audit logs for auth, admin, and provisioning events

8) A simple data model to start with

You’ll likely need tables/objects like:

• users
• tenants
• memberships
• roles
• permissions
• role_permissions
• tenant_idp_connections
• scim_connections
• audit_events

9) My recommendation if you want the shortest path

If you’re building a B2B multi-tenant SaaS and want to get to market quickly:

• Use a managed identity provider or identity bridge
• Implement tenant-based RBAC
• Support OIDC SSO first
• Add SAML next if enterprise demand requires it
• Add SCIM for provisioning
• Keep authorization in your app, not just in the IdP

If you want, I can help you with either:

1. a reference architecture for this setup,
2. a data model/schema for tenants, roles, and memberships, or
3. a build-vs-buy comparison for Auth0, WorkOS, Okta, Cognito, and FusionAuth.