Client
API
API Contract
Client asks. API responds. Your UI updates.
Auth answers: "Who are you?" Access control answers: "What can you do?"

Why Authentication Exists

Without auth, any app could read or modify private data. Authentication proves identity. Authorization controls permissions.

API Keys for Server-to-Server

API keys are simple shared secrets. They work well for trusted backend integrations but should never be exposed in public clients.

Bearer Tokens for User Sessions

Bearer tokens are often short-lived and represent signed user sessions. They are sent in the Authorization header.

Handle Expired Tokens

When tokens expire, APIs return 401. Your app should refresh or ask the user to sign in again, not crash silently.

Scopes Limit Access

Scopes are permission slices like `read:users` or `write:orders`. A token can be valid but still forbidden for some operations.

Store Secrets Carefully

Keep tokens in secure storage, rotate secrets, and never commit them to source control. Security is part of API design, not an afterthought.

Auth Flow Under Control

You understand how keys, tokens, and permissions protect APIs and how frontend apps should react when auth fails.

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