code: func NewMultiHandler(signers map[string]signer.Signer, defaultLabel string) (http.Handler, error) {
  	return &api.HTTPHandler{
  		Handler: &MultiHandler{
  			signers:      signers,
  			defaultLabel: defaultLabel,
  		},
  		Methods: []string{"POST"},
  	}, nil
  }
docs: // NewMultiHandler constructs a MultiHandler from a mapping of labels
  // to signers and the default label.