POC done!

composer.json

@@ -0,0 +1,6 @@
+{
+    "require": {
+        "phly/http": "^0.14.1",
+        "guzzlehttp/guzzle": "~6.0"
+    }
+}

proxy.php

@@ -0,0 +1,55 @@
+<?php
+
+use Phly\Http\Response;
+use GuzzleHttp\Client;
+use Phly\Http\ServerRequestFactory;
+use Phly\Http\ServerRequest;
+
+require __DIR__.'/vendor/autoload.php';
+
+function send(Response $response)
+{
+    http_response_code($response->getStatusCode());
+
+    foreach ($response->getHeaders() as $header => $values) {
+        header(sprintf('%s: %s', $header, implode(', ', $values)));
+    }
+
+    echo $response->getBody();
+}
+
+function doRequest(ServerRequest $request, Client $client)
+{
+    $headers = [];
+
+    foreach ($request->getHeaders() as $name => $value) {
+        $headers[$name] = $value[0];
+    }
+
+    $url = sprintf(
+        'https://bittrex.com/api/v1.1/%s',
+        ltrim($request->getServerParams()['PATH_INFO'], '/')
+    );
+
+    unset($headers['host']);
+
+    return $client->request(
+        $request->getMethod(),
+        $url,
+        [
+            'headers' => $headers,
+            'body' => $request->getBody(),
+        ]
+    );
+}
+
+$apiResponse = doRequest(
+    ServerRequestFactory::fromGlobals(),
+    new Client()
+);
+
+send(new Response(
+    $apiResponse->getBody(),
+    $apiResponse->getStatusCode(),
+    $apiResponse->getHeaders()
+));