jdk.internal.net.http.PlainProxyConnection is never reused by HttpClient

A DESCRIPTION OF THE PROBLEM :
Due to the way the PlainProxyConnection creates its CacheKey (new ConnectionPool.CacheKey(null, address), where address is the proxy's address), the Connection will never be retrieved from the HttpClient's ConnectionPool, as HttpConnection.getConnection() is never called with addr == null.

As a consequence of this behaviour, it is impossible to implement NTLM proxy authentication client side.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Send a number of requests through a proxy from the same HttpClient, sequentially.
Dump the network traffic.



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
All requests are sent using the same port, i.e. the same connection.
ACTUAL -
For each request, a new socket is opened using the next port in queue.

CUSTOMER SUBMITTED WORKAROUND :
None.

FREQUENCY : always