Hi there, good question! We're planning on using Cloudflare Workers for the API Gateway (great edge performance, simple programming & deployment model). we also have plans to allow customers to run their own code to modify requests and responses in the "gateway" by using Cloudflare Workers for Platforms.
Here has one solution (Apache APISIX) just for reference: https://news.ycombinator.com/item?id=32937696
P.S The website is beautiful and attractive! Especially the How it works section.