Authentication
Proving who you are to a system.
Definition
Authentication is the process of verifying a user's identity — confirming they are who they claim to be. Passwords, API keys, OAuth tokens, and biometrics are all authentication methods. It answers the question "who are you?" while authorization (a related concept) answers "what are you allowed to do?"
Example
When you log into GitHub with your username and password, that is authentication. When GitHub then checks whether you have permission to push to a specific repository, that is authorization.
See it in context Learn how Authentication fits into the bigger picture of how software actually works.
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