Add Cookbook C01-C19 (draft)

docs-src/pages/en/cookbook/c16-proxy.md

@@ -0,0 +1,52 @@
+---
+title: "C16. Send Requests Through a Proxy"
+order: 16
+status: "draft"
+---
+
+To route traffic through a corporate network or a specific path, send requests via an HTTP proxy. Just pass the proxy host and port to `set_proxy()`.
+
+## Basic usage
+
+```cpp
+httplib::Client cli("https://api.example.com");
+cli.set_proxy("proxy.internal", 8080);
+
+auto res = cli.Get("/users");
+```
+
+The request goes through the proxy. For HTTPS, the client uses the CONNECT method to tunnel through — no extra setup required.
+
+## Proxy authentication
+
+If the proxy itself requires authentication, use `set_proxy_basic_auth()` or `set_proxy_bearer_token_auth()`.
+
+```cpp
+cli.set_proxy("proxy.internal", 8080);
+cli.set_proxy_basic_auth("user", "password");
+```
+
+```cpp
+cli.set_proxy_bearer_token_auth("token");
+```
+
+If cpp-httplib is built with OpenSSL (or another TLS backend), you can also use Digest authentication for the proxy.
+
+```cpp
+cli.set_proxy_digest_auth("user", "password");
+```
+
+## Combine with end-server authentication
+
+Proxy authentication is separate from authenticating to the end server (C05, C06). When both are needed, set both.
+
+```cpp
+cli.set_proxy("proxy.internal", 8080);
+cli.set_proxy_basic_auth("proxy-user", "proxy-pass");
+
+cli.set_bearer_token_auth("api-token"); // for the end server
+```
+
+`Proxy-Authorization` is sent to the proxy, `Authorization` to the end server.
+
+> **Note:** cpp-httplib does not read `HTTP_PROXY` or `HTTPS_PROXY` environment variables automatically. If you want to honor them, read them in your application and pass the values to `set_proxy()`.