I determined that if I define the payload_content_type as 'text/plain' through python then I no longer see the error.  Also, if I define the payload_content_type as 'application/pkix-cert' on the CLI, I get the same error that I was seeing from python.


From CLI:
~/devstack$ barbican secret get http://localhost:9311/v1/secrets/8ec681e6-145d-4e72-99c7-8a354af6696f --payload -f value --debug --payload_content_type application/pkix-cert
Starting new HTTP connection (1): 10.109.24.227
Starting new HTTP connection (1): localhost
4xx Client error: Not Acceptable
Not Acceptable
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/cliff/app.py", line 314, in run_subcommand
    result = cmd.run(parsed_args)
  File "/usr/local/lib/python2.7/dist-packages/cliff/display.py", line 92, in run
    column_names, data = self.take_action(parsed_args)
  File "/opt/stack/python-barbicanclient/barbicanclient/barbican_cli/secrets.py", line 68, in take_action
    (entity.payload,))
  File "/opt/stack/python-barbicanclient/barbicanclient/secrets.py", line 188, in payload
    self._fetch_payload()
  File "/opt/stack/python-barbicanclient/barbicanclient/secrets.py", line 259, in _fetch_payload
    payload = self._api._get_raw(payload_url, headers=headers)
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 79, in _get_raw
    return self.request(path, 'GET', *args, **kwargs).content
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 63, in request
    self._check_status_code(resp)
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 103, in _check_status_code
    status
HTTPClientError: Not Acceptable
Traceback (most recent call last):
  File "/usr/local/bin/barbican", line 10, in <module>
    sys.exit(main())
  File "/opt/stack/python-barbicanclient/barbicanclient/barbican.py", line 310, in main
    return barbican_app.run(argv)
  File "/opt/stack/python-barbicanclient/barbicanclient/barbican.py", line 305, in run
    return super(Barbican, self).run(argv)
  File "/usr/local/lib/python2.7/dist-packages/cliff/app.py", line 241, in run
    result = self.run_subcommand(remainder)
  File "/usr/local/lib/python2.7/dist-packages/cliff/app.py", line 314, in run_subcommand
    result = cmd.run(parsed_args)
  File "/usr/local/lib/python2.7/dist-packages/cliff/display.py", line 92, in run
    column_names, data = self.take_action(parsed_args)
  File "/opt/stack/python-barbicanclient/barbicanclient/barbican_cli/secrets.py", line 68, in take_action
    (entity.payload,))
  File "/opt/stack/python-barbicanclient/barbicanclient/secrets.py", line 188, in payload
    self._fetch_payload()
  File "/opt/stack/python-barbicanclient/barbicanclient/secrets.py", line 259, in _fetch_payload
    payload = self._api._get_raw(payload_url, headers=headers)
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 79, in _get_raw
    return self.request(path, 'GET', *args, **kwargs).content
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 63, in request
    self._check_status_code(resp)
  File "/opt/stack/python-barbicanclient/barbicanclient/client.py", line 103, in _check_status_code
    status
barbicanclient.exceptions.HTTPClientError: Not Acceptable
~/devstack$ 


From python:
>>> certificate = barbican.secrets.get('http://localhost:9311/v1/secrets/8ec681e6-145d-4e72-99c7-8a354af6696f', payload_content_type='text/plain')
>>> certificate.payload_content_type
'text/plain'
>>> certificate.payload
u'-----BEGIN CERTIFICATE-----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\npQDNWViJBf2Edx32bUOHqnaZ4UIwzig=\n-----END CERTIFICATE-----\n'
>>>