Functions as a Security Layer

Functions, with some databases, are used as security
layers so that a user that wouldn't otherwise have
read/write privileges on a table can perform some sort
of controlled update.

I've written a function to serve as a type of counter
to update a table called "users". This function takes
one (relevant) parameter: userID. This then updates
the counter with that user's id. However, I am getting
a permissions error because the users who run the
function don't have write access to the counter table.

My question is, can I somehow give permissions to the
function, but not to the user to protect the counter
table from being modified in any ways I don't want?

Thanks,
-Ben

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