JWT (JSON Web Token)

A signed, compact token that carries claims about a user, such as who they are and when the token expires.

A JWT has three base64url parts: header, payload and signature. Anyone can read the payload; the signature only proves it was not changed, so secrets do not belong inside. Because servers can verify it without a database lookup, it cannot easily be revoked before it expires, which is why access tokens are kept short-lived and paired with refresh tokens.

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Related terms

OAuth: A standard that lets an app act on a user’s account elsewhere (mail, calendar, files) without ever seeing the password.
CSRF (cross-site request forgery): Another site making a logged-in user’s browser send a request to your app, which the app trusts because the cookie came along.
SSO (single sign-on): Logging in once with a company account (Microsoft, Google, Okta) to use many apps, managed centrally by IT.

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