diff --git a/api/authentication.go b/api/authentication.go
index 792e6e2..bbac2c9 100644
--- a/api/authentication.go
+++ b/api/authentication.go
@@ -242,6 +242,14 @@ func authenticateRequest(w http.ResponseWriter, r *http.Request, targetHandler h
 }
 
 func checkAuth(w http.ResponseWriter, r *http.Request, authRequired bool) (token *AuthToken, handled bool) {
+	// Return highest possible permissions in dev mode.
+	if devMode() {
+		return &AuthToken{
+			Read:  PermitSelf,
+			Write: PermitSelf,
+		}, false
+	}
+
 	// Check for valid API key.
 	token = checkAPIKey(r)
 	if token != nil {
@@ -462,7 +470,12 @@ func deleteSession(sessionKey string) {
 }
 
 func isReadMethod(method string) bool {
-	return method == http.MethodGet || method == http.MethodHead
+	switch method {
+	case http.MethodGet, http.MethodHead, http.MethodOptions:
+		return true
+	default:
+		return false
+	}
 }
 
 func parseAPIPermission(s string) (Permission, error) {
diff --git a/api/config.go b/api/config.go
index 706f5b4..ebcc515 100644
--- a/api/config.go
+++ b/api/config.go
@@ -19,6 +19,8 @@ var (
 	defaultListenAddress string
 
 	configuredAPIKeys config.StringArrayOption
+
+	devMode config.BoolOption
 )
 
 func init() {
@@ -79,6 +81,8 @@ func registerConfig() error {
 	}
 	configuredAPIKeys = config.GetAsStringArray(CfgAPIKeys, []string{})
 
+	devMode = config.Concurrent.GetAsBool(config.CfgDevModeKey, false)
+
 	return nil
 }
 
diff --git a/api/endpoints.go b/api/endpoints.go
index c977fee..bdb068d 100644
--- a/api/endpoints.go
+++ b/api/endpoints.go
@@ -256,6 +256,9 @@ func (eh *endpointHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		apiRequest.InputData = inputData
 	case http.MethodGet:
 		// Nothing special to do here.
+	case http.MethodOptions:
+		w.WriteHeader(http.StatusNoContent)
+		return
 	default:
 		http.Error(w, "Unsupported method for the actions API.", http.StatusMethodNotAllowed)
 		return
@@ -308,7 +311,6 @@ func (eh *endpointHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Write response.
 	w.Header().Set("Content-Type", apiEndpoint.MimeType+"; charset=utf-8")
 	w.Header().Set("Content-Length", strconv.Itoa(len(responseData)))
-	w.Header().Set("X-Content-Type-Options", "nosniff")
 	w.WriteHeader(http.StatusOK)
 	_, err = w.Write(responseData)
 	if err != nil {
diff --git a/api/router.go b/api/router.go
index 81154a5..6b2280c 100644
--- a/api/router.go
+++ b/api/router.go
@@ -16,17 +16,6 @@ var (
 	// gorilla mux
 	mainMux = mux.NewRouter()
 
-	// middlewares
-	middlewareHandler = &mwHandler{
-		final: mainMux,
-		handlers: []Middleware{
-			ModuleWorker,
-			LogTracer,
-			RequestLogger,
-			authMiddleware,
-		},
-	}
-
 	// main server and lock
 	server      = &http.Server{}
 	handlerLock sync.RWMutex
@@ -46,18 +35,12 @@ func RegisterHandleFunc(path string, handleFunc func(http.ResponseWriter, *http.
 	return mainMux.HandleFunc(path, handleFunc)
 }
 
-// RegisterMiddleware registers a middle function with the API endoint.
-func RegisterMiddleware(middleware Middleware) {
-	handlerLock.Lock()
-	defer handlerLock.Unlock()
-	middlewareHandler.handlers = append(middlewareHandler.handlers, middleware)
-}
-
 // Serve starts serving the API endpoint.
 func Serve() {
 	// configure server
 	server.Addr = listenAddressConfig()
 	server.Handler = &mainHandler{
+		// TODO: mainMux should not be modified anymore.
 		mux: mainMux,
 	}
 
@@ -134,6 +117,22 @@ func (mh *mainHandler) handle(w http.ResponseWriter, r *http.Request) error {
 		return nil
 	}
 
+	// Add security headers.
+	if !devMode() {
+		w.Header().Set(
+			"Content-Security-Policy",
+			"default-src 'self'; "+
+				"style-src 'self' 'unsafe-inline'; "+
+				"img-src 'self' data:",
+		)
+		w.Header().Set("Referrer-Policy", "no-referrer")
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		w.Header().Set("X-Frame-Options", "deny")
+		w.Header().Set("X-XSS-Protection", "1; mode=block")
+	} else {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+	}
+
 	// Handle request.
 	switch {
 	case handler != nil: