HTTP proxy - expect 100 and authentication

Question

I have an issue with Apache2 which I use as a proxy. My software sends HTTP PUT for protected resource with

Expect: 100-continue

Transfer-Encoding: chunked

And instead of getting '401 Unauthorized' I get '100 Continue'. After that my soft sends all chunks to server and then I get 401.

It looks like Apache does not forward headers and automatically sends '100 Continue'.

Is this correct behavior?

Here is what I found here

If a proxy receives a request that includes an Expect request-
    header field with the "100-continue" expectation, and the proxy
    either knows that the next-hop server complies with HTTP/1.1 or
    higher, or does not know the HTTP version of the next-hop
    server, it MUST forward the request, including the Expect header
    field

Answer 1

This question was asked already on stackoverflow.com ( https://stackoverflow.com/questions/3889574/apache-and-mod-proxy-not-handling-http-100-continue-from-client-http-417 ):

You could configure it this way:

<IfModule mod_headers.c>
  RequestHeader unset Expect early
</IfModule>

This will remove the Expect header, and the communication should work.

EDIT Please make sure, that the remote side is HTTP/1.1. In the same RFC you linked there is just one page after your cite this:

  - If the proxy knows that the version of the next-hop server is
    HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
    respond with a 417 (Expectation Failed) status.