Senior Backend Engineer – IAM, OAuth & Multi-Tenant Authorization

Our client is facing a crucial year and is now looking for a senior backend developer with deep expertise in Identity & Access Management. This is a key role where you will own and shape the authorization model in a complex multi-tenant environment, and where your technical decisions will have a direct impact across the entire platform. We are not looking for someone who has just used OAuth. We are looking for someone who has designed permission structures in detail, and who can explain why a model should be built in a specific way. This is what you will do: Design and model advanced authorization models for multi-tenant SaaS, including B2B and B2B2B scenarios where customers have their own customers. Specify permission structures: roles, scopes, policies, entitlements, and hierarchies. Implement authentication and authorization in distributed microservice environments. Standardize access control through internal frameworks and libraries that other teams build upon. Ensure secure-by-design and compliance in safety-critical systems. Work closely with architecture, product, and security to build scalable and robust access management. Who we think you are: You have several years of experience with IAM and have modeled complex authorization structures in practice, not just configured ready-made solutions. You have a strong backend background in Java and are accustomed to performance-critical microservice environments. You have a good understanding of OAuth2, token flows, PKI, and established security patterns, and you have worked with multi-tenant architecture in B2B.