The passwordcheck module checks users' passwords
whenever they are set with
CREATE ROLE or
ALTER ROLE.
If a password is considered too weak, it will be rejected and
the command will terminate with an error.
To enable this module, add '$libdir/passwordcheck'
to shared_preload_libraries in
postgresql.conf, then restart the server.
You can adapt this module to your needs by changing the source code.
For example, you can use
CrackLib
to check passwords — this only requires uncommenting
two lines in the Makefile and rebuilding the
module. (We cannot include CrackLib
by default for license reasons.)
Without CrackLib, the module enforces a few
simple rules for password strength, which you can modify or extend
as you see fit.
To prevent unencrypted passwords from being sent across the network, written to the server log or otherwise stolen by a database administrator, PostgreSQL allows the user to supply pre-encrypted passwords. Many client programs make use of this functionality and encrypt the password before sending it to the server.
This limits the usefulness of the passwordcheck
module, because in that case it can only try to guess the password.
For this reason, passwordcheck is not
recommended if your security requirements are high.
It is more secure to use an external authentication method such as GSSAPI
(see Chapter 20) than to rely on
passwords within the database.
Alternatively, you could modify passwordcheck
to reject pre-encrypted passwords, but forcing users to set their
passwords in clear text carries its own security risks.