Assembly Identity Security

Hi, I would appreciate any pointers on a good approach to the following code security scenario.

I have a planned service running extensible packets in a manner like MSBuild e.g. the service picks up packages which includes package task configuration data and a target reference to an assembly responsible for executing the task. The service will execute the task according to supplied credentials.

How would I go about verifying assembly identities. I may know some target execution assemblies for V1 but more will be added following deployment of V1. So I am really looking for an interface trust approach by which I can test target assemblies against a measure of security.