Securing a REST API is a layered process covering transport encryption, authentication, authorization, and input handling, each addressing a different class of attack rather than any single control being sufficient on its own.
Key Points: • Enforce HTTPS everywhere so credentials and payloads can't be intercepted in transit. • Add authentication (OAuth2, JWT, or Basic over TLS) so only verified identities can call the API. • Layer authorization on top—role- or scope-based checks per endpoint—so authenticated users only reach what they're permitted to. • Validate and sanitize all input to prevent injection attacks and malformed data from reaching business logic. • Add rate limiting, logging, and monitoring to detect abuse and give visibility into security-relevant events.
Example: An API first forces all traffic over HTTPS, requires a valid OAuth2 access token on every request, checks the token's scopes against the requested operation, and validates the request body against a strict schema before processing it.
Interview Tip: A concise interview answer is:
"I'd secure it step by step: HTTPS for encryption in transit, then an authentication mechanism like OAuth2 or JWT to verify identity, then role- or scope-based authorization on each endpoint, and finally input validation to block injection attacks. Logging and rate limiting round it out for visibility and abuse prevention."