func (d *DNSProvider) Present(domainName, token, keyAuth string) error {
	fqdn, value := dns01.GetRecord(domainName, keyAuth)
	zone, err := dns01.FindZoneByFqdn(fqdn)
	if err != nil {
		return fmt.Errorf("netcup: failed to find DNSZone, %w", err)
	}
	sessionID, err := d.client.Login()
	if err != nil {
		return fmt.Errorf("netcup: %w", err)
	}
	defer func() {
		err = d.client.Logout(sessionID)
		if err != nil {
			log.Print("netcup: %v", err)
		}
	}()
	hostname := strings.Replace(fqdn, "."+zone, "", 1)
	record := internal.DNSRecord{
		Hostname:    hostname,
		RecordType:  "TXT",
		Destination: value,
		TTL:         d.config.TTL,
	}
	zone = dns01.UnFqdn(zone)
	records, err := d.client.GetDNSRecords(zone, sessionID)
	if err != nil {
		log.Infof("no existing records, error ignored: %v", err)
	}
	records = append(records, record)
	err = d.client.UpdateDNSRecord(sessionID, zone, records)
	if err != nil {
		return fmt.Errorf("netcup: failed to add TXT-Record: %w", err)
	}
	return nil
}
Present creates a TXT record to fulfill the dns-01 challenge.
package netcup
import (
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"
	"github.com/go-acme/lego/v4/challenge/dns01"
	"github.com/go-acme/lego/v4/log"
	"github.com/go-acme/lego/v4/platform/config/env"
	"github.com/go-acme/lego/v4/providers/dns/netcup/internal"
)
const (
	envNamespace = "NETCUP_"
	EnvCustomerNumber = envNamespace + "CUSTOMER_NUMBER"
	EnvAPIKey         = envNamespace + "API_KEY"
	EnvAPIPassword    = envNamespace + "API_PASSWORD"
	EnvTTL                = envNamespace + "TTL"
	EnvPropagationTimeout = envNamespace + "PROPAGATION_TIMEOUT"
	EnvPollingInterval    = envNamespace + "POLLING_INTERVAL"
	EnvHTTPTimeout        = envNamespace + "HTTP_TIMEOUT"
)
type Config struct {
	Key                string
	Password           string
	Customer           string
	TTL                int
	PropagationTimeout time.Duration
	PollingInterval    time.Duration
	HTTPClient         *http.Client
}
func NewDefaultConfig() *Config {
	return &Config{
		TTL:                env.GetOrDefaultInt(EnvTTL, dns01.DefaultTTL),
		PropagationTimeout: env.GetOrDefaultSecond(EnvPropagationTimeout, 120*time.Second),
		PollingInterval:    env.GetOrDefaultSecond(EnvPollingInterval, 5*time.Second),
		HTTPClient: &http.Client{
			Timeout: env.GetOrDefaultSecond(EnvHTTPTimeout, 10*time.Second),
		},
	}
}
type DNSProvider struct {
	client *internal.Client
	config *Config
}
func NewDNSProvider() (*DNSProvider, error) {
	values, err := env.Get(EnvCustomerNumber, EnvAPIKey, EnvAPIPassword)
	if err != nil {
		return nil, fmt.Errorf("netcup: %w", err)
	}
	config := NewDefaultConfig()
	config.Customer = values[EnvCustomerNumber]
	config.Key = values[EnvAPIKey]
	config.Password = values[EnvAPIPassword]
	return NewDNSProviderConfig(config)
}
func NewDNSProviderConfig(config *Config) (*DNSProvider, error) {
	if config == nil {
		return nil, errors.New("netcup: the configuration of the DNS provider is nil")
	}
	client, err := internal.NewClient(config.Customer, config.Key, config.Password)
	if err != nil {
		return nil, fmt.Errorf("netcup: %w", err)
	}
	client.HTTPClient = config.HTTPClient
	return &DNSProvider{client: client, config: config}, nil
}