[xmlsec] Signing using HMAC: how to input shared key

[Aleksey Sanin]

http://www.aleksey.com/xmlsec/api/xmlsec-xmldsig.html#XMLSECDSIGCTX

xmlSecKeyPtr signKey 	
the signature key; application may set signKey before calling 
xmlSecDSigCtxSign or xmlSecDSigCtxVerify functions.


Aleksey