yum commands accessing the Certificate-based RHN content delivery network (CDN) via HTTP proxy are encountering '[Errno 14] HTTP Error ...'

Issue

• Registering and subscribing the system to Certificate-based RHN via the proxy works fine. However yum commands accessing https://cdn.redhat.com always fail with any of the following errors:

    [Errno 14] HTTP Error 501: Not Implemented ... or ...  
    [Errno 14] HTTP Error 503: Service Unavailable ... or ...  
    [Errno 14] HTTP Error 400: Bad Request

• yum is failing on system registered with Red Hat Subscription Manager via http proxy with below mentioned errors:

yum update
Loaded plugins: product-id, security, subscription-manager
Updating Red Hat repositories.
https://cdn.redhat.com/content/dist/rhel/server/5/5Server/x86_64/cf-tools/1/os/repodata/repomd.xml: [Errno 14] HTTP Error 503: Service Unavailable
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: rhel-5-server-cf-tools-1-rpms. Please verify its path and try again

• Unregistering the system via the proxy logs the follwing error on rhsm.log

[INFO]  @connection.py:194 - using proxy 
[INFO]  @connection.py:201 - handler: https://subscription.rhn.redhat.com:443/subscription/consumers/4b0735e9-56c9-4628-8791-3d2c90b3802b/certificates/serials
[INFO]  @connection.py:215 - status code: 502
[ERROR]  @connection.py:227 - No JSON object could be decoded
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/rhsm/connection.py", line 225, in validateResponse
    parsed = json.loads(response['content'])
  File "/usr/lib64/python2.4/site-packages/simplejson/__init__.py", line 307, in loads
    return _default_decoder.decode(s)
  File "/usr/lib64/python2.4/site-packages/simplejson/decoder.py", line 335, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib64/python2.4/site-packages/simplejson/decoder.py", line 353, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded
[ERROR]  @connection.py:229 - remote server status code: 502
[ERROR]  @certmgr.py:96 - Error while updating certificates using daemon