MD5 salt

How do I send an MD5 password to pgsql?  (I'm programming my own front-end)

Pgsql provides a 4-byte 'salt', that you must somehow use with your
password for MD5.  The trouble is, I don't know how.

I have been trying sending the MD5 digest from (password + salt), or
from (salt + password), but it doesn't work.  How exactly does the
salt fit in the picture?

Thanks,

Marc