For Apple Mac Safari
The issue is seems is
on the apple/safari/security side of things.
The recommended fix below works most of the time.
Let me know if this works with your users that are experiencing the
"required certificate issue".
1) Find the
Keychain Access program on your Mac. To find it, open up Finder, then open up the Applications folder, and inside the Applications folder there is
a folder called Utilities, Keychain Access is in the
2) Open Keychain Access and search for all of the
certificates that are listed in Safari dialog box that tells you "This
client requires a certificate".
3) When you find those particular certificates, select
them and then DELETE those specific certificates out of Keychain Access.
4) Then restart Safari, and go back to
It should work from there, if you get the same error
message, repeat the steps and make sure your remove the corrupt certificates.
If you need Apple verification for this issue check out
the link below