RADIUS attribute from rfc5090

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Digest-Realm

This attribute describes a protection space component of the
         RADIUS server.  HTTP-style protocols differ in their definition
         of the protection space.  See, for
         details.  It MUST only be used in Access-Request, Access-
         Challenge, and Accounting-Request packets.
   Type
         104 for Digest-Realm
   Length
         >= 3
   Text
         In Access-Requests, the RADIUS client takes the value of the
         realm directive (realm-value according to ) without
         surrounding quotes from the HTTP-style request it wants to
         authenticate.  In Access-Challenge packets, the RADIUS server
         puts the expected realm value into this attribute.

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