If you do not mind to have the password stored on the computer (otherwise you should use
http://mercurial.selenic.com/wiki/KeyringExtension) it is normally enought to put the auth tag into your .hg/hgrc text file. I added the other tags, in case your need authorization on some of the other aspects too.
[auth]
example.prefix = https://yourdomain.be/yourerpository/
example.username = Userke
example.password = Paswoordje
[paths]
default = https://yourdomain.be/yourerpository/
[http_proxy]
user = Userke
passwd = Paswoordje
[ui]
username = Userke
[reviewboard]
user = Userke
password = Paswoordje