Why do you want to build this over one of the many choices out there:

  https://getkong.org/
  https://lyft.github.io/envoy/
  https://aws.amazon.com/api-gateway/
  https://cloud.google.com/endpoints/
  https://www.ca.com/us/products/ca-api-gateway.html
  https://www.3scale.net/technical-overview/

There's a lot of options out there across the spectrum so just curious what your end goals are