@Override
    public HttpURLConnection getConnection(URL url) throws IOException {
      HttpURLConnection connection = (HttpURLConnection) url.openConnection(this.proxy);
      if (isNotBlank(this.credentials)) {
        connection.addRequestProperty(PROXY_AUTHORIZATION, this.credentials);
      }
      return connection;
    }
Client that supports a {@link java.net.Proxy}.
core/src/main/java/feign/Client.java