CAS Authentication

So I have recently tried authenticating to a cas server for a project,
and every time I try to access my cas server it returns

SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B:
certificate verify failed

Now I am using the CAS gem found here

I know the certificate on the CAS server is valid and correct, and i am
new to RoR
any help?