1. A computer-implemented method, comprising: receiving source code and one or more headers corresponding to a web page requested by a client device; using one or more physical processors, rendering the source code to generate rendered code; using one or more of the physical processors, processing the rendered code to identify one or more security vulnerabilities including identification of an unsecure channel corresponding to a resource identified by the source code; wherein processing the rendered code includes identifying a first reference in the source code to the resource to retrieve the resource via the unsecure channel; using one or more of the physical processors, automatically modifying, responsive to processing the rendered code, one or both of the source code and the one or more headers thereby generating modified code, including inserting first code in the source code, the first code being configured to access the resource or content associated with the resource via a secure channel; wherein modifying the source code includes removing the first reference to the resource, adding a second reference to the resource specifying a security directive requiring use of the secure channel by a browser on the client device, and causing the resource to be hosted on a secure server or domain; and transmitting the modified code to the client device.