How to allocate a global variable (to implement virutal databases)

I would like to implement a row-level security for application-level-user (the user is not a postgresql user), I wish to restrict access to rows in diferent tables based on this application-level-user. My idea is to use rules to rewrite queries based on the contents of a global variable that is set with the application-level-userid, to this end I like to set the variabale at connection-time only, and aplied to all queris by the rewrite rules.

 

I think I can write a c-function but I do not know the correct way to allocate memory with session duration, maybe simply with alloc (o should I use palloc?).

 

Or is there a solution I do not know about?

 

Thanks.