Spring Session is a library that provides a robust, pluggable session management solution for Spring-based applications. It abstracts session storage behind a `SessionRepository` interface, supporting multiple backends including Redis, JDBC, and in-memory. The library seamlessly integrates with both Servlet and WebFlux stacks, replacing the standard `HttpSession` with a configurable, cluster-friendly alternative. It also offers deep integration with Spring Security for concurrent session control and remember-me authentication, and with WebSocket for session-aware messaging. The architecture is modular: `spring-session-core` defines the core API (Session, SessionRepository, FindByIndexNameSessionRepository, HttpSessionIdResolver) and provides the servlet filter (`SessionRepositoryFilter`) and reactive store (`SpringSessionWebSessionStore`). `spring-session-data-redis` implements Redis-backed repositories with support for indexing by principal name and expiration via sorted sets and keyspace notifications. `spring-session-jdbc` provides a JDBC-backed repository with dialect-specific SQL schemas and customizable queries. Configuration is annotation-driven (e.g., `@EnableRedisHttpSession`, `@EnableJdbcHttpSession`) and supports customization through beans like `CookieSerializer`, `SessionRepositoryCustomizer`, and `FlushMode`/`SaveMode`. Key data flows involve session creation, attribute modification, expiration, and principal-based lookup. The library uses events (`SessionCreatedEvent`, `SessionDeletedEvent`, `SessionExpiredEvent`) for lifecycle notifications and supports AOT compilation for GraalVM native images. External dependencies include Spring Framework, Spring Data Redis, Spring Data JDBC, Reactor, and optionally Jackson for JSON serialization. The build system uses Gradle with custom convention plugins for publishing, documentation, and release management.