Sign an S/MIME message
Function pkcs7_sign (infilename As String, outfilename As String, signcert, privkey, [headers], [flags], [extracerts]) As Boolean
pkcs7_sign() takes the contents of the file named infilename
and signs them using the certificate and it's matching private key specified by signcert
and privkey parameters.
headers is an array of headers that will be
prepended to the data after it has been signed (see pkcs7_encrypt()
for more information about the format of this parameter.
flags can be used to alter the output - see
PKCS7 constants - if not specified, it defaults
extracerts specifies the name of a file
containing a bunch of extra certificates to include in the signature which can
for example be used to help the recipient to verify the certificate that you