feat: add support for basic auth (#16)

Add new CLI parameters to enable protecting the API endpoints with basic
auth authentication.
Wrap the server endpoints in a new authMiddleware that protects it using
the provided basic auth credentials (if set).

src/cfg/cfg.go

@@ -18,6 +18,8 @@ type AppSettings struct {
 	Fail2BanSocketPath   string
 	FileCollectorPath    string
 	FileCollectorEnabled bool
+	BasicAuthUsername    string
+	BasicAuthPassword    string
 }
 
 func Parse() *AppSettings {
@@ -28,6 +30,8 @@ func Parse() *AppSettings {
 	flag.StringVar(&appSettings.Fail2BanSocketPath, "socket", "", "path to the fail2ban server socket")
 	flag.BoolVar(&appSettings.FileCollectorEnabled, "collector.textfile", false, "enable the textfile collector")
 	flag.StringVar(&appSettings.FileCollectorPath, "collector.textfile.directory", "", "directory to read text files with metrics from")
+	flag.StringVar(&appSettings.BasicAuthUsername, "web.basic-auth.username", "", "set username for basic auth")
+	flag.StringVar(&appSettings.BasicAuthPassword, "web.basic-auth.password", "", "set password for basic auth")
 
 	flag.Parse()
 	appSettings.validateFlags()

src/exporter.go

@@ -48,6 +48,21 @@ func metricHandler(w http.ResponseWriter, r *http.Request, collector *textfile.C
 	collector.WriteTextFileMetrics(w, r)
 }
 
+func authMiddleware(handlerFunc http.HandlerFunc, appSettings *cfg.AppSettings) http.HandlerFunc {
+	authEnabled := len(appSettings.BasicAuthUsername) > 0 && len(appSettings.BasicAuthPassword) > 0
+	if authEnabled {
+		return func(w http.ResponseWriter, r *http.Request) {
+			username, password, ok := r.BasicAuth()
+			if !ok || username != appSettings.BasicAuthUsername || password != appSettings.BasicAuthPassword {
+				w.WriteHeader(http.StatusUnauthorized)
+				return
+			}
+			handlerFunc.ServeHTTP(w, r)
+		}
+	}
+	return handlerFunc
+}
+
 func main() {
 	appSettings := cfg.Parse()
 	if appSettings.VersionMode {
@@ -63,10 +78,13 @@ func main() {
 		textFileCollector := textfile.NewCollector(appSettings)
 		prometheus.MustRegister(textFileCollector)
 
-		http.HandleFunc("/", rootHtmlHandler)
-		http.HandleFunc(metricsPath, func(w http.ResponseWriter, r *http.Request) {
+		http.HandleFunc("/", authMiddleware(rootHtmlHandler, appSettings))
+		http.HandleFunc(metricsPath, authMiddleware(
+			func(w http.ResponseWriter, r *http.Request) {
 				metricHandler(w, r, textFileCollector)
-		})
+			},
+			appSettings,
+		))
 		log.Printf("metrics available at '%s'", metricsPath)
 
 		svrErr := make(chan error)