data access automatic filter

Hi,

I'm evaluating the option of write a PG-extension which allow the
application to apply some per-connection filters. This filters work at
table level and remove records which aren't allowed from a select
result-set.

Example:
CREATE CONNECTION DATA FILTER my_filter CHECKING my_table.my_field=5;

A "SELECT * FROM my_table" will only return all the rows with
"field=5"

Could someone tell me which is the PG source files which I could
change?

TIA

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