RADIUS attribute from rfc5090

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Digest-Username

This attribute holds the user name used in the HTTP Digest
         calculation.  The RADIUS server MUST use this attribute only
         for the purposes of calculating the digest.  In order to
         determine the appropriate user credentials, the RADIUS serverMUST use the User-Name (1) Attribute, and MUST NOT use the
         Digest-Username Attribute.  This attribute MUST only be used in
         Access-Request and Accounting-Request packets.
   Type
         115 for Digest-Username
   Length
         >= 3
   Text
         In Access-Requests, the RADIUS client takes the value of the
         username directive (username-value according to )
         without surrounding quotes from the HTTP-style request it wants
         to authenticate.

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