How would you design a scalable API gateway for multiple microservices that provides load balancing, authentication, and request routing? What considerations should be taken into account for scalability?

``` I would implement an API gateway using a lightweight proxy like NGINX or Envoy to handle incoming requests, providing services such as rate limiting, authentication token validation, and routing requests based on URL patterns. Scenario Pressure: Discuss the impact of onboarding additional microservices on the gateway's performance and the need for horizontal scaling. Depth Trigger: Explain how you would secure the API gateway and manage user access across different microservices. ```