How do I force apache to send the Content-Length header for Docker?

Since Docker client versions under 1.8.x do not send the content-length header, it causes Docker push to fail with Artifactory 4.x (& 3.9.4)  + Docker < 1.8. You can add the following directive to your VirtualHost in order to force apache to send this header - 

    SetEnv                  proxy-sendcl 1