title: Add cookie to response with OkHttp3 / Retrofit
body: <p>I am trying to add a header to HTTP responses. This is my Interceptor which is not working:</p>
  
  <pre><code>builder.addInterceptor(new Interceptor() {
      @Override
      public Response intercept(Chain chain) throws IOException {
          Request request = chain.request();
  
          Request addedTestRequest = request.newBuilder().addHeader("TEST", "test").build();
  
          Response response = chain.proceed(addedTestRequest);
  
          final Response addedTestResponse = response.newBuilder().addHeader("TEST", "test").build();
  
          return addedTestResponse;
      }
  });
  </code></pre>
  
  <p>I can see the header TEST in outgoing traffic (requests) but <strong>not in incoming traffic (responses)</strong>. Do you know what is the problem or is there another way to add headers to responses?</p>
  
  <p>Note: I am using <a href="https://github.com/franmontiel/PersistentCookieJar" rel="nofollow noreferrer">franmontiel/PersistentCookieJar</a> with OkHttp3 / Retrofit, if that influences anything. </p>