What methods can be used to verify user identity in a system?

User identity verification (authentication) in a system can be implemented using the following methods:

• Password and login — the most common method, where the user enters a unique identifier and a secret (password).
• Two-factor authentication (2FA) — in addition to the password, a code from SMS, an authenticator app, or a hardware token is required.
• Biometric authentication — using fingerprints, facial recognition, voice.
• OAuth and social networks — login through third-party services (Google, Facebook, etc.), where authentication is delegated.
• Tokens and sessions — after successful login, a token (e.g., JWT) is issued to the user, confirming identity for subsequent requests.

Example of a simple login and password check in Python:

users = {'user1': 'password123'}

def authenticate(username, password):
    if username in users and users[username] == password:
        return True
    return False

print(authenticate('user1', 'password123'))  # True
print(authenticate('user1', 'wrongpass'))    # False