This feature is rather old but I just found out about it. If you have a LiveJournal or SimilarJournal (InsaneJournal at least) and you have access to ‘friends-locked’ posts but you’d like to be able to pick them up in your normal feed reader, you can very likely use a URL like this:
http://YOURUSERNAME:PASSWORD@THEIRUSERNAME.livejournal.com/data/atom?auth=digest
For communities use the community URL followed by /data/atom?auth=digest. Similarly for LJ-like sites with their own URLs. You can also replace atom with rss if you are that way inclined.
This is described in FAQ 149 on LiveJournal.
If using a reader that is implemented in Python (eg Planet and Venus, rss2email) you will probably need to make sure you are using Python 2.5 underneath rather than any earlier version of Python, as Python’s urllib2 did not work with LiveJournal’s Digest-Auth implementation until just after Python 2.4 was released.
If this doesn’t work in your reader, the feature you want them to add and test is called ‘HTTP digest authentication’. There may also be some alternative way they want you to put in ‘YOURUSERNAME’ and ‘PASSWORD’.