authenticateUser

AuthenticateUser is a function or process used to verify the claimed identity of a user. It typically takes credentials such as a username or user identifier and a secret (most commonly a password), but may also accept tokens, API keys, or biometric proofs. The primary goal is to confirm that the claimant possesses knowledge or data that only the legitimate user should have.

In web and application contexts, authenticateUser is invoked during login flows. The function usually retrieves the user record by identifier, compares the provided secret against a securely stored representation (for passwords, a salted hash using algorithms such as bcrypt, Argon2, or PBKDF2), and, on success, creates a session or issues an authentication token (for example a JWT) to be presented in subsequent requests. It distinguishes between authentication (proof of identity) and authorization (permissions).

Variants include multi-factor authentication, step-up challenges, and passwordless methods such as magic links or device-based tokens. Some implementations integrate with external identity providers using protocols like OAuth 2.0 or OpenID Connect, where authenticateUser delegates to the provider.

Security considerations include using strong password hashing with salts and slow hashing, implementing rate limiting and account lockout policies, monitoring for abuse, and secure storage of secrets. Transport layer security should be enforced to protect credentials in transit. Error messages should avoid revealing whether a username exists, and session management and token revocation should be properly implemented to maintain ongoing access control.

See also: authentication, password hashing, MFA, OAuth 2.0, OpenID Connect, token-based authentication.