Fix withCore overriding request core options when using withAuth

[leelaprasadv]

Summary

• Closes sequence of methods is important but not described or relevant #344
• withCore method was overriding the core options of request object, fix is to extend/override using deep-override instead of direct assignment.
• After this fixwithCore and withAuth sequence in chaining can be shuffled.

Note: if withCore is used at the end of the request chaining, options in withCore (if provided) will override in http request.