If this is a duplicate I apologize.

ISTM this requires

• Move all uses of httplib2 into a module (call it transport probably) (Plan to Implement: oauth2client.transport module #554, Begin transport module for httplib2 specific pieces. #559, Remove httplib2 parts from service_account module. #561, Remove httplib2 imports from non-transport modules. #577)
• Determine what assumed interface of httplib2.Http is needed
• Optional. Try to reduce the interface needed
• Factor out the hard dependencies on httplib2 and just use these interfaces
• Document the interface and allow credentials constructors to optionally take a custom Http object from any old library, e.g. twisted or requests.
• Revisit all changes and ensure consistency
• Revisit query string update hackery in Correct query loss when using parse_qsl to dict #622