RADIUS attribute from rfc2865
This Attribute indicates the name of the user to be authenticated. It MUST be sent in Access-Request packets if available. It MAY be sent in an Access-Accept packet, in which case the client SHOULD use the name returned in the Access-Accept packet in all Accounting-Request packets for this session. If the Access- Accept includes Service-Type = Rlogin and the User-Name attribute, a NAS MAY use the returned User-Name when performing the Rlogin function. A summary of the User-Name Attribute format is shown below. The fields are transmitted from left to right. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- | Type | Length | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Type 1 for User-Name. Length >= 3 String The String field is one or more octets. The NAS may limit the maximum length of the User-Name but the ability to handle at least 63 octets is recommended. The format of the username MAY be one of several forms: text Consisting only of UTF-8 encoded 10646 characters. network access identifier A Network Access Identifier as described in. distinguished name A name in ASN.1 form used in Public Key authentication systems.