My ASP.NET MVC application has been successfully ported to Mono. It works very well in xsp on port 8080, including the OpenID authorization process which is relying on RPX. In the process, the website makes some calls to RPX API (https://rpxnow.com/api/v2/...) in the background. At first, it triggered a HTTP 500 error in xsp. The problem has been solved by simply executing once the "mozroots --import --sync --quiet" command to install certificates on the server.
Now I am trying to configure Apache with mod_mono to make the same site work on port 80. To my surprise, the HTTP 500 problem has resurfaced while trying to authenticate a test user. This time, I cannot figure out how to get rid of it. It seems that there is something missing in apache's configuration files.