Partner credentials

[gavinhodge]

There's a fair bit in this PR... Summary of changes:

• Rework Public Credentials
  • Allow RSA signing of requests and client side certificates, but this can't be turned on via the PublicCredentials constructor.
  • Base url is now an instance variable (needed later for partner credentials)
  • Store the token expiry date and provide expired() to check if token is still valid
  • There are no breaking changes - PublicCredentials work as normal
• Create Partner Credentials
  • Inherits PublicCredentials, constructor allows RSA cert and client side cert
  • Changes the base url to the partner one
  • Adds refresh() function to gain a new token
• Manager
  • Construct with credentials object instead of oauth.
  • Endpoint URLs are built using base url from credentials
  • Pass client side certificate to requests

This is a cleaned up version of a fork that's been used in production for a few months.

[aidanlister]

Wow, great patch, everything looks pretty good, and thanks for the test coverage. @freakboy3742 I'll defer to you :)

[aidanlister]

I made this a bit tougher for myself than it needed to be by applying a bunch of other commits first and then spending several hours resolving conflicts, but I have tested the functionality and it works as expected, the test suite passes, and my own integration still functions so I'm going to merge this in now.

[gavinhodge]

Ouch, sorry this stole hours of your time! Thanks for looking it over, much appreciated.

[aidanlister]

No worries, thank you muchly for contributing your well written and tested code back!