You can.
The FreeRADIUS site has this.
Also, in Debian.
Package: freeradius-postgresql
Priority: optional
Section: net
Installed-Size: 196
Architecture: amd64
Source: freeradius
Version: 2.0.4+dfsg-6
Depends: freeradius (= 2.0.4+dfsg-6), libc6 (>= 2.7-1), libpq5 (>= 8.3~beta1)
Filename: pool/main/f/freeradius/freeradius-postgresql_2.0.4+dfsg-6_amd64.deb
Size: 37508
MD5sum: 2aa09c0767dce7be1a5bc8afa95d3191
SHA1: c4c1f36f5ba5e0e52a6e78b55f2e409e9e867323
SHA256: 326c3550d60fb08e26414b1de64ca0ed410118c6a0e9a7024906d0b9c1ae21f1
Description: PostgreSQL module for FreeRADIUS server
The FreeRADIUS server can use PostgreSQL to authenticate users and do
accounting, and this module is necessary for that.
Tag: implemented-in::c, protocol::radius, role::plugin, security::authentication, works-with::db
FreeRADIUS is a quality piece of software and while I don't use it anymore (we use Radiator) it will do the job for you nicely.
Ben