API security protects web services from unauthorized access, data breaches, and abuse. As APIs become the primary interface for applications and services, securing them is critical. APIs expose business logic and data, making them attractive targets for attackers. Understanding API security threats and implementing appropriate controls ensures APIs remain secure while serving legitimate users.

Authentication Methods

API Keys are simple identifiers included in requests (typically in headers or query parameters). They identify API clients and are easy to implement but have limitations: they’re bearer tokens (anyone with the key has access), difficult to rotate safely, and lack fine-grained permissions.

Authentication and authorization are foundational security concepts that control who can access systems and what they can do. Authentication verifies identity—proving you are who you claim to be. Authorization determines permissions—what you’re allowed to do once identified. Understanding these concepts and implementing them correctly is essential for building secure applications and protecting sensitive data.

Authentication: Proving Identity

Username and Password authentication is the most common method. Users provide credentials, which the system validates against stored hashes (never plaintext passwords). While familiar, password authentication has weaknesses: users choose weak passwords, reuse passwords across sites, and phishing attacks steal credentials.

Encryption transforms readable data into unintelligible ciphertext using mathematical algorithms and keys, protecting confidentiality from unauthorized access. Whether protecting data in transit over networks or at rest in storage, encryption is fundamental to modern security. Understanding encryption types, algorithms, and best practices enables protecting sensitive information effectively while avoiding common mistakes that undermine security.

Symmetric Encryption

Symmetric encryption uses the same key for both encryption and decryption. This is fast and efficient but requires secure key distribution since anyone with the key can decrypt data.

JSON Web Tokens (JWT) are compact, URL-safe tokens that represent claims between parties. JWTs encode information in JSON format, cryptographically sign it, and optionally encrypt it, enabling stateless authentication and information exchange. Their self-contained nature makes JWTs popular for API authentication, single sign-on, and distributed systems where maintaining server-side session state is impractical.

Structure

JWTs consist of three parts separated by dots: Header, Payload, and Signature.

Header describes the token type (JWT) and signing algorithm (like HMAC SHA256 or RSA). This metadata enables receivers to validate tokens correctly.

OAuth 2.0 is an authorization framework enabling applications to obtain limited access to user resources without exposing credentials. Instead of sharing passwords with third-party applications, users authorize specific permissions, and applications receive access tokens for API requests. OAuth has become the standard for delegated authorization, powering “Sign in with Google/Facebook/GitHub” features and API integrations across the web.

Core Concepts

Resource Owner is the user who owns data and can grant access to it. For example, you own your Google photos and can authorize applications to access them.