How to specify the operational requirement in bindings ?

Hi,

Regarding how a simple web services can be aggregated in complex real-life 
scenario, any thoughts on how one can specify a certain operation of a 
particular port type requires the caller to be authenticated and possess 
certain security tokens ?  Or how to specify if the operation has to be 
called within an already established conversation (some sort of correlation 
properties) ?  Or how to specified if the operation has to be called within 
a transaction (so the invoker has to pass in the "transaction context" and 
a registration service so that the service provider can be enrolled in the 
transaction as a participant) ?

Best regards,
Ricky