PostgreSQL versions lower than 11 come bundled with chkpass extension for storing encrypted passwords. This was removed from Postgres 11 and later. This is a stand alone version for use with those.

See documentaion for chkpass.

Install appropriate Postgres server development package

apt-get install postgresql-server-dev-12

To build and install this module:

make
make install
make install installcheck

or selecting a specific PostgreSQL installation:

make PG_CONFIG=/some/where/bin/pg_config
make PG_CONFIG=/some/where/bin/pg_config install
make PG_CONFIG=/some/where/bin/pg_config installcheck
make PGPORT=5432 PG_CONFIG=/usr/lib/postgresql/12/bin/pg_config clean install installcheck

Make sure you set the connection parameters like PGPORT right for testing.

And finally inside the database:

CREATE EXTENSION chkpass;