code: func (p *OpenPrinter) Auth() Auth {
  	if p.verify == nil {
  		panic(fmt.Errorf("Auth: VerifyClaim has not succeeded"))
  	}
  	return p.auth
  }
docs: // Auth returns a credential that can be used to manage this printer
  // in future invocations of the program.
  //
  // Auth must be called only after VerifyClaim has succeeded.