http://www.rfc-editor.org/rfc/rfc7542.txt
RFC 7542: The Network Access Identifier, A. DeKok2015-05-01T23:00:00-00:00In order to provide inter-domain authentication services, it is necessary to have a standardized method that domains can use to identify each other's users. This document defines the syntax for the Network Access Identifier (NAI), the user identifier submitted by the client prior to accessing resources. This document is a revised version of RFC 4282. It addresses issues with international character sets and makes a number of other corrections to RFC 4282.