Parameters for the XML Signature HMAC Algorithm.

  Parameters for the
XML Signature HMAC Algorithm. The parameters include an optional output
length which specifies the MAC truncation length in bits. The resulting
HMAC will be truncated to the specified number of bits. If the parameter is
not specified, then this implies that all the bits of the hash are to be
output. The XML Schema Definition of the HMACOutputLength
element is defined as:

 <element name="HMACOutputLength" minOccurs="0" type="ds:HMACOutputLengthType"/>
 <simpleType name="HMACOutputLengthType">
   <restriction base="integer"/>
 </simpleType>