In a guest post by Serge Bakharev, the challenges and best practices of implementing Identity and Access Management (IAM) within microservice architectures are discussed. The complexity arises from the need for multiple independent services to authenticate and authorize requests consistently, without compromising the Single Responsibility Principle. Instead of relying on a central dependency, a multilayered IAM approach is recommended, with access policies enforced at both the edge via an Access Server and closer to the microservice itself. This dual-layer strategy, advocated by standards like NIST 800-204, ensures security by requiring failures at both levels before unauthorized access can occur. Stateless tokens, particularly JSON Web Tokens (JWT), are favored for their ability to decouple authentication from authorization, enabling validation throughout the infrastructure without dependency on session state information. The use of external authentication providers and API gateways with token filtering capabilities simplifies the implementation of such access policies, allowing for role-based access control and fine-grained policies within the microservices.