Implement simple basic auth.

Closes #326.

helpers.go

@@ -51,6 +51,46 @@ func ensureDELETE(handler func(http.ResponseWriter, *http.Request)) func(http.Re
 	return ensure("DELETE", handler)
 }
 
+func optionalAuth(handler func(http.ResponseWriter, *http.Request)) func(http.ResponseWriter, *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if config.AuthName == "" || config.AuthPass == "" {
+			handler(w, r)
+			return
+		}
+		user, pass, ok := r.BasicAuth()
+		if !ok || user != config.AuthName || pass != config.AuthPass {
+			w.Header().Set("WWW-Authenticate", `Basic realm="dnsfilter"`)
+			w.WriteHeader(http.StatusUnauthorized)
+			w.Write([]byte("Unauthorised.\n"))
+			return
+		}
+		handler(w, r)
+	}
+}
+
+type authHandler struct {
+	handler http.Handler
+}
+
+func (a *authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if config.AuthName == "" || config.AuthPass == "" {
+		a.handler.ServeHTTP(w, r)
+		return
+	}
+	user, pass, ok := r.BasicAuth()
+	if !ok || user != config.AuthName || pass != config.AuthPass {
+		w.Header().Set("WWW-Authenticate", `Basic realm="dnsfilter"`)
+		w.WriteHeader(http.StatusUnauthorized)
+		w.Write([]byte("Unauthorised.\n"))
+		return
+	}
+	a.handler.ServeHTTP(w, r)
+}
+
+func optionalAuthHandler(handler http.Handler) http.Handler {
+	return &authHandler{handler}
+}
+
 // --------------------------
 // helper functions for stats
 // --------------------------