HTTP Post with Parameter and Body

Try using below code inside a function node. Of course you want to replace the data otherwise the API will not authenticate.

The HTTP request node should have the Method field configured as "-set by msg.method-"

msg.headers = {}
msg.method = "POST"
msg.url = "https://arche.webuntis.com/WebUntis/jsonrpc.do" ;
msg.headers["content-type"] = "application/json"


msg.payload = {
"id":"ID",
"method":"authenticate",
"params":
{
"user":"xy",
"password":"PASSWORD",
"client":"CLIENT"
},
"jsonrpc":"2.0"
};

return msg