OAuth2orize
OAuth 2.0 authorization server toolkit for Node.js
...It integrates with Express and similar frameworks, letting developers define how clients are authenticated, how authorization decisions are made, and how tokens are issued, all through a clean, extensible API. The module encourages a modular design where individual grant types are plugged in as needed, enabling only relevant flows for a given application, such as supporting third-party app access without exposing user credentials. It also provides helpers for serializing clients and users into session state, signing tokens, and validating requests, reducing the boilerplate developers would otherwise write.