It's no surprise to anyone who has visited my blog before that I have had InfoCard support within Serendipity for some time now. Serendipity was not originally designed with third party authentication mechanisms in mind, so in order to allow for this, I had to heavily modify the internals of the code. Although an external authentication plugin has been available, it simply allows a username/password combination to be validated by an outside source. This combination is then saved in the Serendipity author table and then pulled from there. Not the best solution (and a simple explanation on my part of how it really works), but in the case of OpenID and InfoCard quite impossible. There are no username/passwords being submitted to the blog. In any event, this made Serendipity upgrades very painful as I had to merge my changes by hand into the new revisions. The problems I had with integration have been the very same issues that has prevented the addition of OpenID support.