adds fritzbox session check and re-authenticate if nesessarry

internal/fritzbox/authentication.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 )
 
 // PerformLogin performs a login and returns SessionInfo including
@@ -34,6 +35,31 @@ func (fb *FritzBox) PerformLogin(adminPassword string) error {
 	return nil
 }
 
+func (fb *FritzBox) CheckSession() (bool, error) {
+	client := fb.getHTTPClient()
+
+	requestBody := strings.NewReader("sid=" + fb.session.SID)
+
+	resp, err := client.Post(fb.Host+"/login_sid.lua?version=2", "application/x-www-form-urlencoded", requestBody)
+	if err != nil {
+		return false, err
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return false, err
+	}
+	defer resp.Body.Close() // nolint: errcheck
+
+	var sessionInfo SessionInfo
+	err = xml.Unmarshal(body, &sessionInfo)
+	if err != nil {
+		return false, err
+	}
+
+	return sessionInfo.SID == fb.session.SID, nil
+}
+
 func fetchSessionInfo(client *http.Client, url string) (SessionInfo, error) {
 	resp, err := client.Get(url)
 	if err != nil {

main.go

@@ -86,6 +86,19 @@ func main() {
 		config.certificateBundle = io.MultiReader(bytes.NewReader(cert.Certificate), bytes.NewReader(cert.PrivateKey))
 	}
 
+	sessionOk, err := fritz.CheckSession()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if !sessionOk {
+		log.Println("Session expired, re-authenticating...")
+		err := fritz.PerformLogin(config.adminPassword)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+
 	// Upload certificate and private key
 	status, response, err := fritz.UploadCertificate(config.certificateBundle)
 	if err != nil {