Bug 1016423 - Use Hawk for making authenticated HTTP requests and support FxA assertions

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1016423 please.
> unpacked is not a JSON? If it is ,why do we need to parse it? Please check if claim exists before trying to access
> to it.

We need to parse 'unpacked.claim' as it is a string.