Microservice applications increase the complexity of authentication, authorization, and session management compared to traditional monolithic architecture, necessitating new approaches for these functions. Authentication in microservices is often handled by a dedicated service that ensures users are authenticated and authorized before processing requests, avoiding the redundancy of implementing authentication in each service. Secure token-based authentication is preferred over basic methods to prevent exposing user credentials, with access tokens enabling a time-limited, stateless mechanism for user verification. Session management in distributed microservices can be challenging, as session data must be accessible across multiple servers or containers. Solutions include using a central data store or API gateway to manage session data, ensuring scalability and security. An API gateway can centralize authentication and manage user sessions using tokens like JSON web tokens (JWT) to maintain a stateless architecture while protecting session details from interception. OAuth is recommended for secure third-party application access, and tools like the Kong API gateway offer plugins to streamline authentication and session management across APIs.