Associate one vendor with a category and then restrict access

[Patrick-4]

I have associated a Party with Role "Vendor" to a Category.  I want
only that vendor to be able to add products to that category.  Is
there a simple way to do this?

The service that is executing is

 <service name="safeAddProductToCategory"

I tried to do something like this
<required-permissions join-type="AND">
   <check-role-member role-type="VENDOR"   />
</required-permissions>

but I don't know how to say "if this user is the vendor of this category"
Thank you very much
Patrick