Authentication techniques are methods used to verify the identity of a user or system. Common techniques include passwords, which require users to enter a secret word or phrase, and biometric authentication, which uses unique physical traits like fingerprints or facial recognition. These methods help ensure that only authorized individuals can access sensitive information. Another popular technique is two-factor authentication (2FA), which adds an extra layer of security by requiring a second form of verification, such as a code sent to a mobile device. Other methods include security tokens and smart cards, which provide physical devices for secure access.