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Pre-provisioning the intermediate CAs has the advantage of a relatively small amount of data being sent during the EAP authentication, which means fewer round-trips between the end-user's device and the eduroam IdP RADIUS server. The downsides of this approach are that any changes to intermediate CAs (re-issue, rollover) will also need to be pushed to end-user devices. Also, if end-user devices are not under administrative control of the IdP, there is a danger that some end users do not follow the advice to install all intermediate CAs even though they shoudl, and end up in a situation where the server certificate can not be validated.
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