Rodauth is a Ruby authentication framework designed as a Roda plugin, but also usable as middleware or a standalone library. It provides a comprehensive, modular authentication system covering login, logout, account creation, password management, multi-factor authentication (TOTP, WebAuthn, SMS, recovery codes), JWT/JSON API support, session management, and many security features like lockout, password complexity, and audit logging. The architecture is built around a declarative feature DSL where each feature is a self-contained module that can be enabled via `plugin :rodauth` and configured with hundreds of overridable methods. The core library defines a `Rodauth::Auth` class instantiated per request, with metaprogramming for hooks, routes, and value methods. The codebase is exceptionally well-crafted, with a clean separation of concerns, extensive use of inheritance and composition, and a strong emphasis on security (HMAC tokens, timing-safe comparisons, database functions for password hashing). It is actively maintained by the author Jeremy Evans with a long history of releases and security fixes.