What are the common ways to secure your API and verify users?

API authentication verifies the identity of clients making requests. Different methods suit different scenarios based on security requirements, client types, and user experience.

API Keys are simple strings included in request headers or query parameters. Easy to implement but limited: they identify the application, not the user, and if compromised, require rotation. Best for server-to-server communication or public APIs with rate limiting.

Session-based authentication stores session data server-side after login, sending a session ID via cookies. Simple and secure for browser applications but requires server-side state management and doesn't work well for mobile apps or cross-domain scenarios.

JWT (JSON Web Tokens) are self-contained tokens containing encoded claims. The server signs them but doesn't need to store them. Clients include the JWT in the Authorization header. JWTs are stateless and work across domains but can't be easily invalidated (use short expiration + refresh tokens).

OAuth 2.0 is an authorization framework for delegated access. Instead of sharing passwords, users authorize applications to act on their behalf. It involves authorization servers, access tokens, and refresh tokens. Essential for "Login with Google/GitHub" flows and when your app needs to access other services on behalf of users.

For most web applications: use JWT or sessions for your own auth, OAuth 2.0 for social login, and API keys for external developer access. Always use HTTPS, implement rate limiting, and follow security best practices for token storage.