Systems, methods, and non-transitory computer-readable storage media for securely accessing locally stored synchronized content using a local web server. A client application on a client device may receive from a web browser on the client device a request to access a local content stored on a client device. The client application may be configured to synchronize the local content with a remote content stored in an online content management system. The client application may issue a challenge for the web browser. The client application or the online content management system may then receive a response to the challenge. If the response is a valid response to the challenge, the web browser may be allowed to access the local content via the client application.