In the subversion repository setup, it will not allow https in the URL field. There is no SSL ability it seems -
Error is: callback_ssl_server_trust_prompt required
I've tried (and failed) to reproduce this using the repo https://svn.blender.org/svnroot/bf-blender/ - it seemed to work OK.
I'm pretty sure I know what's required to fix the problem you're seeing, but could you please provide:
1. the log extract, including stack trace, from the error above, and
2. an HTTPS repo URL that I can test this against.
Thanks in advance ....................... JD