Most SaaS API breaches begin with the object, not the firewall_

OWASP lists broken object-level authorization as a leading API risk. Multi-tenant systems are especially exposed when an authenticated user can change an ID and reach another tenant’s record.

Authentication proves who sent the request. It does not prove that person can read or modify the requested customer, invoice, report, or workflow.

What changes in practice_

Enforce tenant and object authorization in every data access path, test cross-tenant identifiers, and avoid trusting tenant IDs supplied by clients.

• Authorize every object access.
• Derive tenant context from trusted identity.
• Include negative cross-tenant tests.

Our take_

The durable advantage is not adopting the newest tool first. It is building the identity, state, evidence, and operating boundaries that let a real team own the system after launch.