Federated Token - Envelop Plugin

This packages provides an Envelop plugin so that for example Yoga can be used as
a federated service. I
It provides three Apollo specific classes:
federatedAuthPlugin - An Apollo plugin for federated services that reads
the token passed in the x-access-token header and stores it on the context
as federatedToken.
When a federated services creates a new token (when non exist) it can also
return a refresh token in the x-refresh-token header. The gateway will then
encrypt all refresh tokens and encrypt them before passing them to the client
as x-refresh-token header.