I have already installed the CERN certificates for my browser (image attached). 
I also joined the MoEDAL VO from : https://voms2.cern.ch:8443/voms/vo.moedal.org/register/start.action and received the confirmation.

After that, as I tried to access the webpage https://dirac.gridpp.ac.uk:8443/DIRAC/ , it opens a blank page with ‘Unauthorized’ written. Could you help me with this?

Thank you!
Best Regards