Servers SHOULD NOT respond to GET requests for registration resources
as these requests are not authenticated. If a client wishes to query
the server for information about its account (e.g., to examine the
"contact" or "certificates" fields), then it SHOULD do so by sending
a POST request with an empty update. That is, it should send a JWS
whose payload is trivial ({"resource":"reg"}). In this case the
server reply MUST contain the same link headers sent for a new
registration, to allow a client to retreive the "new-authorization"
and "terms-of-service" URI
(But I am not sure if Let's Encrypt/Boulder actually implement this empty request idea).