scripts: added mavlink signing key to secure_command.py

this allows for secure_command.py over support.ardupilot.org signed remote link

scripts/secure_command.py

@@ -22,6 +22,7 @@ parser.add_argument("--node-id", default=100, type=int, help="local CAN node ID"
 parser.add_argument("--target-node", default=None, type=int, help="target node ID")
 parser.add_argument("--private-key", default=None, type=str, help="private key file")
 parser.add_argument("--bus-num", default=1, type=int, help="MAVCAN bus number")
+parser.add_argument("--signing-passphrase", help="MAVLink2 signing passphrase", default=None)
 parser.add_argument("uri", default=None, type=str, help="CAN URI")
 parser.add_argument("paramop", default=None, type=str, help="parameter operation")
 args = parser.parse_args()
@@ -50,6 +51,9 @@ last_set_config = 0
 node = dronecan.make_node(args.uri, node_id=args.node_id, bitrate=args.bitrate)
 node.can_driver.set_bus(args.bus_num)
 
+if args.signing_passphrase is not None:
+    node.can_driver.set_signing_passphrase(args.signing_passphrase)
+
 # Initializing a node monitor
 node_monitor = dronecan.app.node_monitor.NodeMonitor(node)