Fix nil key bug in AMQP mode.

wfe/web-front-end.go

@@ -574,6 +574,12 @@ func (wfe *WebFrontEndImpl) Registration(response http.ResponseWriter, request *
 		return
 	}
 
+	// Registration objects contain a JWK object, which must be non-nil. We know
+	// the key of the updated registration object is going to be the same as the
+	// key of the current one, so we set it here. This ensures we can cleanly
+	// serialize the update as JSON to send via AMQP to the RA.
+	update.Key = currReg.Key
+
 	// Ask the RA to update this authorization.
 	updatedReg, err := wfe.RA.UpdateRegistration(currReg, update)
 	if err != nil {