code: func (d *DNSProvider) Present(domain, _, keyAuth string) error {
  	// Compute the challenge response FQDN and TXT value for the domain based
  	// on the keyAuth.
  	fqdn, value := dns01.GetRecord(domain, keyAuth)
  
  	// Check if credentials were previously saved for this domain.
  	account, err := d.storage.Fetch(domain)
  	// Errors other than goacmeDNS.ErrDomainNotFound are unexpected.
  	if err != nil && err != goacmedns.ErrDomainNotFound {
  		return err
  	}
  	if err == goacmedns.ErrDomainNotFound {
  		// The account did not exist. Create a new one and return an error
  		// indicating the required one-time manual CNAME setup.
  		return d.register(domain, fqdn)
  	}
  
  	// Update the acme-dns TXT record.
  	return d.client.UpdateTXTRecord(account, value)
  }
docs: // Present creates a TXT record to fulfill the DNS-01 challenge.
  // If there is an existing account for the domain in the provider's storage
  // then it will be used to set the challenge response TXT record with the ACME-DNS server and issuance will continue.
  // If there is not an account for the given domain present in the DNSProvider storage
  // one will be created and registered with the ACME DNS server and an ErrCNAMERequired error is returned.
  // This will halt issuance and indicate to the user that a one-time manual setup is required for the domain.