RADIUS attribute from rfc5090


If this attribute is present in an Access-Request message, a
         RADIUS server implementing this specification MUST treat the
         Access-Request as a request for Digest Authentication.  When a
         RADIUS client receives a (Proxy-)Authorization header, it puts
         the request-digest value into a Digest-Response Attribute.
         This attribute (which enables the user to prove possession of
         the password) MUST only be used in Access-Request packets.Type
         103 for Digest-Response.
         >= 3
         When using HTTP Digest, the text field is 32 octets long and
         contains a hexadecimal representation of a 16-octet digest
         value as it was calculated by the authenticated client.  Other
         digest algorithms MAY define different digest lengths.  The
         text field MUST be copied from request-digest of digest-
         response  without surrounding quotes.