To provide improved security in adjunct program modules such as plug-ins and dynamic link libraries, a requesting module provides an authorization interface to the invoked module such that the invoked module can require a certificate of the requesting module and can also challenge the authority of the requesting module. The certificate can include one or more permissions which are prerequisites for processing by the invoked module. The invoked module can challenge the authority of the requesting module by sending random test data to the requesting module and receiving in response a cryptographic signature of the test data. By verifying the signature of the requesting module using the received certificate, the invoked module confirms that the requesting module is, in fact, the owner of the receive certificate.