Added support to send custom headers to upstream servers.

Cargo.lock

@@ -2478,6 +2478,7 @@ dependencies = [
  "bytes",
  "encoding_rs",
  "futures-core",
+ "futures-util",
  "h2",
  "http",
  "http-body",
@@ -2499,12 +2500,14 @@ dependencies = [
  "sync_wrapper",
  "tokio",
  "tokio-native-tls",
+ "tokio-util",
  "tower",
  "tower-http",
  "tower-service",
  "url",
  "wasm-bindgen",
  "wasm-bindgen-futures",
+ "wasm-streams",
  "web-sys",
 ]
 
@@ -3499,6 +3502,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "wasm-streams"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15053d8d85c7eccdbefef60f06769760a563c7f0a9d6902a13d35c7800b0ad65"
+dependencies = [
+ "futures-util",
+ "js-sys",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "web-sys",
+]
+
 [[package]]
 name = "web-sys"
 version = "0.3.77"