APIs continue to play a significant role in modern web development, driving innovation across various sectors, but they also represent a vulnerable area for organizations due to exposed application logic and sensitive data. To mitigate this risk, authentication is required to verify the identity of users making API requests, while authorization verifies the properties or information that verified users can access. Transport Layer Security (TLS) provides encryption and mutual authentication for select organizations using zero trust security models, OAuth 2.0 offers a secure way for users to grant third-party applications access to their resources without sharing passwords, JSON Web Tokens (JWTs) provide key-based client authentication with self-contained tokens that eliminate the need for additional calls to retrieve user information or check permissions, and rate limiting prevents excessive or malicious traffic from abusing APIs. The choice of API authentication method depends on specific needs, and understanding these methods is essential for protecting API resources and sensitive data.