Classloader design and signed code

Hi everyone

I am currently working on a classloader and I want to know how signed code is check.
In a policy file you can specify a signer. Then when a class is loaded it will check the digital signature in the class-file before granting the permission.
I don't really know how this works with a classloader. Does it have something to do with the parameters you pass to defineClass method in the classloader?

thanks in advance