What is Token?
In authentication, a token is an opaque or self-contained string issued to a client after login, presented on subsequent requests to prove identity without resending credentials each time. Tokens can be opaque references the server looks up (like a session ID) or self-contained and verifiable (like a JWT), which avoids a database lookup per request.
Example
An Authorization: Bearer <token> HTTP header is the standard way to send an access token.
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