Current Apple iOS versions have already integrated the required CA-certificates into the operation system. If you use an older version, the easiest way to get the required certificates is to download them from an existing network entrance.
Provided, the two certificates have already been installed, you will receive according feedback from the system.
Now, execute the Wi-Fi configuration as described below.
Settings / Wi-Fi: eduroam
Apple iOS does not know the root certificate of the German Telekom (Deutsche Telekom Root CA2) for encrypted communication. Thus, you will need to adopt the following certificates of these servers:
In the south building in Wilhelmshaven, the following certificate needs to be adopted:
In the canteen / computing centre building in Oldenburg, the following certified needs to be adopted:
In case you are not asked for a username, you will need to delete the existing eduroam profile on your smartphone, first.