Add JWT Support to Gateway

[GeorgeMac]

OSS now allows for JWT token validation in http API. We need to update to this latest version and wire in a signing key in order to validate tokens from future to() transformations.

Steps

1. Update to version of OSS which support jsonweb package.
2. Create implementation of jsonweb.KeyStore which provides a signing key from an environment var.
3. Create suitable environment variable for signing key (e.g. GATEWAY_JWT_SIGNING_KEY).
4. Configure AuthenticationHandler with a jsonweb.TokenParser which uses env var KeyStore implementation.

Success Criteria

With the appropriate signing key a token can be generated and access authorized via gateway.

[russorat]

fyi @pierwill