Is it possible to make HTTP call from fn on_http_request_headers method?

[Igor Androsov]

Use case for this is custom Auth policy for Envoy often needs to make additional validation HTTP requests to IDP services as example to validate header values or possibly chain 2 calls to get final OK to Continue.

Looking at on_http_request_headers function and Rust HTTP Client calls it seem those are not compatible even if we use reqwest::blocking::Client. Is this something that can be done in the context of WASM custom policy for Envoy or NOT?
Using this sample code inside a function while it works in Rust code it does not seem to be compatible with proxi-wasm ABI

let client = Client::new();
let resp = client.post("http://httpbin.org/post")
.body("Send secret code to validate")
.send()?;
if resp.status() == StatusCode::OK {
println!("RESULT 200");
return Action::Continue;
}else{
println!("RESULT ERROR");
}

This code cannot compile due to errors like this one of them cannot use the ? operator in a method that returns proxy_wasm::types::Action

[Piotr Sikora]

It possible to make HTTP calls (see: examples/http_auth_random.rs), but not using reqwest::blocking::Client.