CMS Verify of any post input

Typical setup:

	AddHandler cgi-script .cgi
	<Location /post-api>
        	SetInputFilter          cmsverify
        	CMSVerifyCertificate    /tmp/ca.cert

		# ProxyPass https://127.0.0.1/api
		# Alias  ... etc.
	</Location>

where this Location is then routed to a ProxyPass or for example rewritten.

And call it with:

	echo "field1=foo&field2=bar" |\
		openssl cms -sign -signer cert.pem -outform DER -nodetach -binary |\ 
		curl -vvv --silent --data-binary - https://127.0.0.1/post-cgi/show.cgi

Where 'show.cgi' is a script such as:
	
	#!/bin/sh
	echo Content-type: text/plain
	echo
	env | sort
	if [ "X$REQUEST_METHOD" = "XPOST" ]; then
		/usr/bin/hexdump -C
	fi
	exit 0

to confirm that this worked. Besides DER PKCS#7 the JSOn format:

	{ "payload": "... base64 string ..", "signature": "... base64 string .." }

is also accepted/detected; with signature a detached signature on the decoded payload string. And the signature
again a PKCS#7 DER once decoded.