Add health-check endpoint

Signed-off-by: Knut Ahlers <knut@ahlers.me>

README.md

@@ -55,6 +55,7 @@ In all cases specify one or more `--vehicle-id` (`VEHICLE_ID=WDB111111ZZZ22222,W
 When everything is running you should be able to access the exporter:
 
 - `https://exporter.example.com/auth` - Redirect to authorize your project to access your car(s)
+- `https://exporter.example.com/healthz` - Health-Check endpoint
 - `https://exporter.example.com/metrics` - Text-version of exported metrics
 
 You need to access the `/auth` route once to fetch access- and refresh-keys. If something wents wrong with those keys you can re-authorize the app using this route.

main.go

@@ -76,6 +76,7 @@ func main() {
 	// Register HTTP handlers
 	http.DefaultServeMux.HandleFunc("/auth", getAuthRedirectHandler(mClient))
 	http.DefaultServeMux.HandleFunc("/store-token", getAuthStoreTokenHandler(mClient, creds))
+	http.DefaultServeMux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) { w.Write([]byte("OK")) })
 	http.DefaultServeMux.Handle("/metrics", promhttp.Handler())
 
 	scheduler := cron.New()