code: func (s tlsSniSolver) Present(domain, token, keyAuth string) error {
  	cert, acmeDomain, err := acme.TLSSNI01ChallengeCert(keyAuth)
  	if err != nil {
  		return err
  	}
  	cacheCertificate(Certificate{
  		Certificate: cert,
  		Names:       []string{acmeDomain},
  	})
  	return nil
  }
docs: // Present adds the challenge certificate to the cache.