Refactoring spec into web API and authenticator model

I just sent out a PR that lays out the approach I alluded to on the previous call. For convenient review, I'm attaching a bikeshed-processed html version to this email. Please take a look and let me know if you have comments or feedback, either by replying to this email or (even better) by commenting on the PR in Github.

Thanks,

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-Vijay