The typ header should be optional in the JWT plugin

[subnetmarco]

Plugin does not handle Bearer tokens that do not have the "typ":"JWT" in the header. Per https://tools.ietf.org/html/rfc7519#section-5 the use of the typ header is optional:

To reproduce, using information from https://getkong.org/plugins/jwt/:

curl http://kong:8001/apis/ \
--data 'request_path=/ifconfig' \
--data 'upstream_url=http://ifconfig.io/' \
--data 'strip_request_path=true'

curl http://kong:8001/apis/ifconfig/plugins \
--data "name=jwt"

curl http://kong:8001/consumers \
--data "username=ui"

curl http://kong:8001/consumers/ui/jwt \
--data "algorithm=HS256" \
--data "key=a36c3049b36249a3c9f8891cb127243c" \
--data "secret=e71829c351aa4242c2719cbfbe671c09"

curl -i http://kong:8000/ifconfig \
-H 'Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhMzZjMzA0OWIzNjI0OWEzYzlmODg5MWNiMTI3MjQzYyIsImV4cCI6MTQ0MjQzMDA1NCwibmJmIjoxNDQyNDI2NDU0LCJpYXQiOjE0NDI0MjY0NTR9.AhumfY35GFLuEEjrOXiaADo7Ae6gt_8VLwX7qffhQN4'

The above works as expected. However, if the header does not include "typ" a 500 error is returned:

curl -i http://kong:8000/ifconfig \
-H 'Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJhMzZjMzA0OWIzNjI0OWEzYzlmODg5MWNiMTI3MjQzYyIsImV4cCI6MTQ0MjQzMDA1NCwibmJmIjoxNDQyNDI2NDU0LCJpYXQiOjE0NDI0MjY0NTR9.AqN3-JN_JZoqqvaOTtb_8QBnqYQ5_tXYsQHBUAsHKak'

A 500 error is returned.

I am using the docker image mashape/kong:0.8.1

[sean-sageify]

Created pull request for change. Tested locally fine.