This issue also pop's up with Lync Meeting, not only with Skype for Business Meetings.
Content was blocked because it was not signed by a valid security certificate
After investigation, I saw this was most likely related to changes in Skype for Business Client Update from Januar 2016: https://support.microsoft.com/en-us/kb/3114502
As I described earlier in my blog: http://lyncuc.blogspot.de/2015/10/wildcard-certificate-support-in-skype.html
It is absolute curial following the infrastructure recommendations from Microsoft, regardless if it might work or not. Once there will be an update released, the not recommended setup will have issues or will fail!
A valid SAN Wildcard certificate could look like this:
CN = fqdn.DOMAIN.COM
SAN = fqdn.DOMAIN.COM
SAN = surl.DOMAIN.COM
SAN = *.DOMAIN.COM
I took a deeper look into the assigned certificate.
Btw, it is also in hybrid Skype for Business setup required to be assigned to a local point of access for simple URL's.
We see the CN (or SN) has FQDN as *.domain.com
next screenshot show's it in detail again.
While the last screenshot show's the wildcard name repeated in the SAN (Subject Alternative Name).
I have seen several environment running this configuration without issues as they told me.
But, how they can trace the join users experience?
True, they can't and here I give the example of a situation,where it ended up in mess.
Please define your Reverse Proxy and your Edge Server certificates in the supported and best practice setup.