Configure Forward Proxying from Edge to a Backend Server

[akashtp]

I have set up my proxy settings based on the guidance here:
http://docs.apigee.com/private-cloud/latest/configure-forward-proxying-edge-backend-server.

conf_http_HTTPClient.use.proxy=false
conf_http_HTTPClient.use.tunneling=false
conf/http.properties+HTTPClient.proxy.type=HTTP
conf/http.properties+HTTPClient.proxy.host=my.host.com
conf/http.properties+HTTPClient.proxy.port=80
conf/http.properties+HTTPClient.proxy.user=<username>
conf/http.properties+HTTPClient.proxy.password=<password>

The settings work to talk to the forwarding proxy, but our network resource says that no proxy credentials are being passed for authentication. Is there some change I need to make?