One embodiment of the present invention provides a method for facilitating secure extension of an application. The method operates by first establishing an agreement between an owner of the application and a third party to allow the third party to incorporate an extension into the application. Once an agreement has been established, the system causes the extension to be digitally signed with a private key associated with the owner of the application, whereby the resulting digital signature can be verified with a corresponding public key to confirm that the extension is authorized to be used by the application. The system also configures the application to operate with extensions signed with the private key. In a variation on this embodiment, causing the extension to be digitally signed involves receiving the extension from the third party and signing the extension with the private key belonging to the owner of the application.