Store database users in custom table

Hi,

I am developping a Java application, and using a PostgreSQL backend
database. Theorically, there might be lots of users, each with
potentially different permissions over the different tables.

I could add those user to the database with a classic CREATE USER, but
that doesn't seem efficient to me, since I've already got a custom table
with users data and, amongst others, password.

So my question is simple (the answer might not be, though): is there a
possibility to tell Postgres to fetch user logins and passwords in a
custom table (perhaps respecting a certain schema) instead of the
default location?

Thank you.

Antoine POPINEAU.