A security gateway security gateway provisions a web browser hosted on a user device with a proxy auto-configuration file configured to automatically redirect the web browser to the security gateway as a proxy server for clientless virtual private network (VPN) operation when the web browser browses any uniform resource locator including a particular domain name that encompasses a private network. Upon receiving from the web browser over a public network a request to access a private resource on the private network, the security gateway establishes a secure public connection to the web browser, establishes a private connection to the private resource, and associate the private connection with the secure public connection to form a clientless VPN connection between the web browser and the private resource. The security gateway forwards content between the private resource and the web browser over the clientless VPN connection without performing any content rewrite operations.