Maximum username length

Hi all, We have a project trying to integrate pfsense and freeradus together to form a captive portal, not rocket science. We're going to attempt to pass a number of delimited variables through via the username field and split them at the freeradius end, mostly to avoid rewriting the php in the captive portal to use more orthodox existing attributes. Can someone confirm the maximum username field length? I can see in the RFCs that 63 is the recommended minimum nas length but there's not much else I can see in there. Thanks Andy