code: func (wfe *WebFrontEndImpl) validPOSTForAccount(
  	request *http.Request,
  	ctx context.Context,
  	logEvent *web.RequestEvent) ([]byte, *jose.JSONWebSignature, *core.Registration, *probs.ProblemDetails) {
  	// Parse the JWS from the POST request
  	jws, prob := wfe.parseJWSRequest(request)
  	if prob != nil {
  		return nil, nil, nil, prob
  	}
  	return wfe.validJWSForAccount(jws, request, ctx, logEvent)
  }
docs: // validPOSTForAccount checks that a given POST request has a valid JWS
  // using `validJWSForAccount`. If valid, the authenticated JWS body and the
  // registration that authenticated the body are returned. Otherwise a problem is
  // returned. The returned JWS body may be empty if the request is a POST-as-GET
  // request.