Problem, early this year: https://discussions.apple.com/thread/4100536?start=0&tstart=0
Three years ago: https://discussions.apple.com/thread/2615197?start=0&tstart=0
Last year: https://discussions.apple.com/thread/3753653?start=0&tstart=0
Last month: https://discussions.apple.com/thread/2537287?start=0&tstart=0
Something could be done on the server side, like this: http://www.amixa.com/blog/2012/07/03/iphone-ipad-cannot-verify-server-identity-ssl-issue-and-resolution/; but Apple is not configurable.