RADIUS attribute from rfc5090

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Digest-Domain

When a RADIUS client has asked for a nonce, the RADIUS server
         MAY send one or more Digest-Domain attributes in its Access-
         Challenge packet.  The RADIUS client puts them into the quoted,
         space-separated list of URIs of the domain directive of a WWW-
         Authenticate header.  Together with Digest-Realm, the URIs in
         the list define the protection space (see ,) for some HTTP-style protocols.  This attribute MUST only
         be used in Access-Challenge and Accounting-Request packets.
   Type
         119 for Digest-Domain
   Length
         3Text
         This attribute consists of a single URI that defines a
         protection space component.

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