I checked SSL support for all BOINC projects yesterday in the following thread:
The users in the thread suggested reaching out to all affected projects, so here I am!
Leiden has an invalid SSL certificate according to ssllabs due to certificate name mismatch: https://www.ssllabs.com/ssltest/analyze.html?d=boinc.gorlaeus.net
Would it be possible to reconfigure your SSL certificate?
I used letsencrypt on my own website & received an A+ rating. It was free and took an hour max to setup a valid HTTPS certificate. https://letsencrypt.org/