sorry but im even more confused now, can or can't i use a 2048 bits certificate for captive portal with version 5.x (to be really specific 5.0.4.13)?
the line you quote says you should be able to for captive portal and webui, while the line i quoted from the same document says you cant use 2048 bits for webui (but mentions nothing about about captive portal).
in my opinion it would be worth for aruba to clarify this in a updated advisory with simple table or such. so per use: webui, captive portal, eap termination and the certificate key size.