one of the documented procedures in this installation of the ACS
util_httppost   url   formvars   { timeout "30" }   { depth "0" }   { http_referer "" }
What it does:
Returns the result of POSTing to another Web server or -1 if there is an error or timeout. formvars should be in the form "arg1=value1&arg2=value2"
Defined in: /web/philip/packages/acs-core/utilities-procs.tcl

Source code:

    if [catch {
	if {[incr depth] > 10} {
		return -code error "util_httppost:  Recursive redirection:  $url"
	set http [util_httpopen POST $url "" $timeout $http_referer]
	set rfd [lindex $http 0]
	set wfd [lindex $http 1]

	#headers necesary for a post and the form variables

	_ns_http_puts $timeout $wfd "Content-type: application/x-www-form-urlencoded \r"
	_ns_http_puts $timeout $wfd "Content-length: [string length $formvars]\r"
	_ns_http_puts $timeout $wfd \r
	_ns_http_puts $timeout $wfd "$formvars\r"
	flush $wfd
	close $wfd

	set rpset [ns_set new [_http_gets $timeout $rfd]]
		while 1 {
			set line [_ns_http_gets $timeout $rfd]
			if ![string length $line] break
			ns_parseheader $rpset $line

	set headers $rpset
	set response [ns_set name $headers]
	set status [lindex $response 1]
	if {$status == 302} {
		set location [ns_set iget $headers location]
		if {$location != ""} {
			ns_set free $headers
			close $rfd
			return [ns_httpget $location $timeout $depth]
	set length [ns_set iget $headers content-length]
	if [string match "" $length] {set length -1}
	set err [catch {
		while 1 {
			set buf [_ns_http_read $timeout $rfd $length]
			append page $buf
			if [string match "" $buf] break
			if {$length > 0} {
				incr length -[string length $buf]
				if {$length <= 0} break
	} errMsg]
	ns_set free $headers
	close $rfd
	if $err {
		global errorInfo
		return -code error -errorinfo $errorInfo $errMsg
    } errmgs ] {return -1}
	return $page