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Single sign-on lets an application rely on an identity provider so users can reuse an established login. OIDC supplies login identity on top of OAuth, while access and refresh tokens support API access and session continuation. The client and API validate different token purposes rather than trusting any token returned by the login service.

A tenant is an organizational identity boundary containing users, applications and policies. Multi-tenant applications must decide which organizations can sign in and which data each organization may access. Identity-provider tenant validation and application database tenant scoping are related but separate controls.

Workflow state records where a run is, which steps completed and what remains to be done. Retries repeat recoverable steps, while compensation performs a business recovery action after partial success. Durable state makes these decisions possible after a process restart instead of relying on in-memory progress.

A stored procedure is database-side code that groups SQL operations and control flow into a callable unit. It can reduce application round trips and centralize data logic, but a procedure can still contain slow queries or hold locks too long. Optimization begins by finding the expensive statements and understanding their plans and transaction behavior.

Price/time priority chooses better eligible prices first and then the earlier accepted order among equal-price orders in a simple matching model. Auditability means accepted inputs and resulting decisions can be reconstructed and checked. Concurrency control, durable sequence and exact quantities are needed so recovery does not change the outcome.

A difficult-problem answer should show how you reasoned under a real constraint, not simply that a project had many features. Pick one problem where your investigation or decision changed the outcome. Keep the story focused enough that you can defend each technical detail.

The interviewer first needs a clear picture of what the product does and who uses it. Introduce the business domain before listing frameworks so the technical discussion has context. A short project summary should be understandable to someone outside your team.