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I work locally also with SSL (testing mostly). Works great, but may I remind you that SSL does not make your script safe or so, it justs encrypt the connection, so people can't read your exchange of data with the server (it it possible, however almost not possible
).
If your XOOPS_URL is set to your https link, ALL links in your XOOPS site will redirect to it, so people won't even notice the change (however, they might ofcourse get a warning they changing from unsecure connection to a secure connection, depending on preferences).