Dictionary term
JWT (JSON Web Token)
Also called JSON Web Token
A compact, URL-safe string that carries claims (such as user id and expiry) as JSON, signed so the receiver can check it hasn't been altered; it has a header, a payload and a signature.
In plain English
A signed digital pass that says who you are and when it expires, which servers can check without looking you up.
Analogy
Like a wristband at an event: staff can see it's genuine and still valid without calling the box office.
Why it matters
Many auth systems, including Supabase, issue JWTs as access tokens; the payload is only encoded, not encrypted, so never put secrets in it.
In practice
Your Next.js app sends the signed-in user's Supabase access token (a JWT) with each request, and Postgres policies read the user id from it.
Related terms
Sources
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