Authentication

The process of verifying that a user is who they claim to be, typically via email/password, magic links, or social login (Google, Apple). Separate from authorisation (what they can do).

Every app with user accounts needs authentication. Getting it wrong exposes user data. Solutions like Supabase Auth, Clerk, or Auth0 let founders implement it securely without building from scratch.

A founder uses Clerk to add authentication to her SaaS in one afternoon. Users can sign up with Google, and Clerk handles the sessions, tokens, and security automatically.