openconnect: allow specifying a custom CSD wrapper script

Some VPN servers might be configured in a way that a CSD wrapper script
is mandatory to complete the authentication process, allow that to be
specified for openconnect.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

net/openconnect/files/openconnect.sh

 	proto_config_add_string "token_secret"
 	proto_config_add_string "interface"
 	proto_config_add_string "os"
+	proto_config_add_string "csd_wrapper"
 	no_device=1
 	available=1
 }
 proto_openconnect_setup() {
 	local config="$1"
 
-	json_get_vars server port username serverhash authgroup password interface token_mode token_secret os
+	json_get_vars server port username serverhash authgroup password interface token_mode token_secret os csd_wrapper
 
 	grep -q tun /proc/modules || insmod tun
 
 	[ -n "$token_mode" ] && append cmdline "--token-mode=$token_mode"
 	[ -n "$token_secret" ] && append cmdline "--token-secret=$token_secret"
 	[ -n "$os" ] && append cmdline "--os=$os"
+	[ -n "$csd_wrapper" ] && [ -x "$csd_wrapper" ] && append cmdline "--csd-wrapper=$csd_wrapper"
 
 	proto_export INTERFACE="$config"
 	logger -t openconnect "executing 'openconnect $cmdline'"