Design and scale Zapier's IAM platform: OAuth/JWT, permissions, service-to-service auth

Interview for a Senior Fullstack Engineer role on Zapier's Identity Platform team, owning the systems that model, enforce, and scale access across the company — permissions, OAuth/JWT infrastructure, and service-to-service authentication. Expect deep platform-engineering questions on IAM design (RBAC/ABAC/ReBAC), stable API/versioning discipline, and cross-team influence, since this is a shared platform other teams depend on.

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What this interview tests

OAuth/JWT infrastructure design: tokens, scopes, signing, key rotation
Authorization models: RBAC, ABAC, relationship-based access control
Service-to-service authentication (client credentials, service identity, token propagation)
Platform engineering discipline: stable APIs, managing breaking changes at scale
Cross-team influence to unify inconsistent auth patterns
Enterprise governance requirements for access control

Common question themes

Design an authorization system for permissions, roles, and policies for a multi-tenant SaaS product

How would you roll out a breaking change to a shared auth SDK used by many teams without an outage

Walk through JWT signing, validation, and key rotation in a distributed system

When would you choose RBAC vs ABAC vs relationship-based access control

Describe unifying inconsistent auth patterns across services you didn't originally build

How do you use AI agents in your day-to-day engineering workflow

How candidates describe it

Real Sr. Engineer interview stories — retold from candidates' public write-ups, with sources.

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