code: func GetX509Certificate(stub ChaincodeStubInterface) (*x509.Certificate, error) {
  	c, err := New(stub)
  	if err != nil {
  		return nil, err
  	}
  	return c.GetX509Certificate()
  }
docs: // GetX509Certificate returns the X509 certificate associated with the client,
  // or nil if it was not identified by an X509 certificate.