JWT explained: what a JSON Web Token is and how it worksWhat a JSON Web Token is, how the header.payload.signature structure works, which claims and algorithms exist, and how to validate JWTs safely.What is authentication? Passwords, biometrics, SSO, and modern methods explainedAuthentication is the process of verifying who you are. Learn how passwords, multi-factor authentication, biometrics, SSO, OAuth, and password managers work — and which methods offer the best protection for your application.How to add JWT authentication to a Node.js API: a practical guideStep-by-step implementation of JWT authentication on a Node.js/Express API: password hashing, login endpoint, token verification middleware, refresh tokens, and the common security pitfalls.What is OAuth 2.0? How OAuth works and how to secure itOAuth 2.0 is an open standard for delegated authorization defined in RFC 6749. It lets a user (the resource owner) grant a third-party application (the client) limited access to resources on another server without sharing their password. This guide explains the four roles, the main grant types, the recommended authorization-code flow with PKCE, and the security best practices from RFC 9700.How to set up SSH key authentication (GitHub + Linux)Set up SSH key authentication for GitHub and Linux servers: generate Ed25519 keys, add to ssh-agent, copy public key, and test connection — step-by-step with open-license sources. 