Logger logs unsent request headers even though Default in Client has restricted headers

Since the default class Default in Client uses sun.net.www.protocol.http.HttpURLConnection, which has the set of restricted headers, even if I add a header using RequestTemplate#header(String, String), the actual HTTP request does not contain the header.

However feign.Logger logs not the actual request but the Request made by SynchronousMethodHandler#executeAndDecode(), which contains the restricted header I have added.

This inconsistency made me hard to discover the problem because there's no such documentation tells the logged request may not be the same as the actual HTTP request.

I hope to add some documentation that tells RequestTemplate you applied may not be the actual request or, if possible, make Logger logs the actual HTTP request.

Start with Default in Client and SynchronousMethodHandler#executeAndDecode(), then trace how RequestTemplate#header(String, String) reaches feign.Logger and the sun.net.www.protocol.http.HttpURLConnection client. Compare the logged Request with the headers sent by the actual HTTP request; done means either documenting this discrepancy clearly or making the logger reflect the sent request.