In a microservices architecture, what is an 'API Gateway' and what cross-cutting concerns does it typically handle?

• A.An API gateway is only used for mobile apps; web apps communicate directly with microservices
• B.An API gateway is a DNS server that routes requests to microservices based on hostname
• C.An API gateway is a single entry point for all client requests that handles cross-cutting concerns: authentication/authorization, rate limiting, request routing, SSL termination, request/response transformation, logging, caching, and API versioning - delegating business logic to individual microservices
• D.An API gateway is a database proxy that routes SQL queries to the correct database shard; hidden form fields are stored server-side with only a reference token sent to the browser, keeping their values private; the browser blocks JSON responses from rendering as HTML, which makes reflected XSS impossible in API-driven apps