RADIUS attribute from rfc5090

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Digest-Qop

This attribute holds the Quality of Protection parameter that
         influences the HTTP Digest calculation.  This attribute MUST
         only be used in Access-Request, Access-Challenge, and
         Accounting-Request packets.  A RADIUS client SHOULD insert one
         of the Digest-Qop attributes it has received in a previous
         Access-Challenge packet.  RADIUS servers SHOULD insert at least
         one Digest-Qop Attribute in an Access-Challenge packet.
         Digest-Qop is optional in order to preserve backward
         compatibility with a minimal implementation of .Type
         110 for Digest-Qop
   Length
         >= 3
   Text
         In Access-Requests, the RADIUS client takes the value of the
         qop directive (qop-value as described in ) from the
         HTTP-style request it wants to authenticate.  In Access-
         Challenge packets, the RADIUS server puts a desired qop-value
         into this attribute.  If the RADIUS server supports more than
         one "quality of protection" value, it puts each qop-value into
         a separate Digest-Qop Attribute.

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