getting online.sdu.dk to work under linux requires installation of a citrix client and to add the global sign root certificate.
A google search will give the certificate but here is a direct link:
copy the certificate and paste it in a file called eg. globalsignrootcertificate.crt and save it in:
/opt/Citrix/ICAClient/keystore/cacerts
make sure that permissions are like the other certificates that is located in that folder(Not sure if it gives problems not to ensure this)