Builds the octet string the HTTP-POST-SimpleSign binding signs: the message base64-decoded, then RelayState and SigAlg.
the form's controls
SAMLRequest or SAMLResponse
SAMLRequest
SAMLResponse
the octets, or '' when a field it needs is missing or repeated
Builds the octet string the HTTP-POST-SimpleSign binding signs: the message base64-decoded, then RelayState and SigAlg.