Custom Proxy for Users in HTTP Request

What I’m trying to do:
I’m building a crypto trading app and the api and secret key has a rate limit for a ip address. so my users will need their own api/secret key and sign up for proxy service that I can make the request with.
Is there a syntax to setup in the header or the http request?

Is there a way to setup a proxy for my rest http request. I don’t see a attribute to add a custom proxy, port, and optional: user authentication.?

What I’ve tried and what’s not working:
look through documentation and searched forums.

In the docs you linked, there’s a parameter for setting HTTP headers. You’d have to set appropriate headers (as per your crypto API service’s specifications) for authentication.