Refactor to add support for OAuth2

[gary-rowe]

After discussions on the Dropwizard email group regarding HMAC, it is clear that OAuth2 offers a better solution to the problem of an authenticated RESTful API than HMAC and has better support within Dropwizard. However, HMAC is much simpler to implement and is the current authentication system of choice.

As part of a later initiative it might be worth looking into a 2-factor authentication approach with the Google Authenticator for a complete solution.

To get OAuth2 working the following needs to occur:

1. Examine the existing dropwizard-auth module for the OAuth2 hooks (see the Dropwizard documentation )
2. Locate a project that demonstrates how to do it (see this GitHub project )
3. Incorporate the necessary support into a fresh branch for this issue, based on current "develop"
4. Provide a collection of functional tests and base classes (like the HMAC support classes) to verify that the OAuth2 handing is correct.