add rack middleware to validate authorization header
add expectation to rack middleware test
make rack middleware actually do what I want it to
add current_user method to BaseController
move refresh_key method into PublicKey#key
add TODO: generate access token for test
sub JSON::JWT methods in rack middleware test
Merge pull request #57 from PRX/current_user

Add current_user method to BaseController

* Add Rack middleware to parse and validate PRX Auth JWTs
* Add current_user method to BaseController which can read the output of the middleware