JSON escape non-ascii characters

Hi,

I´m using Newtonsoft JSON on my c# application and it has the option to escape non-ascii characters when serializing an object.

Here are some simple examples: (using the Newtonsoft JSON library in c#)

string obj = "abcn\n\rüö&/<>"; 
Console.WriteLine(Serialize(obj, StringEscapeHandling.Default)); 
Console.WriteLine(Serialize(obj, StringEscapeHandling.EscapeHtml)); 
Console.WriteLine(Serialize(obj, StringEscapeHandling.EscapeNonAscii));

I'm having a hard time finding any similar functionality using Swift.

This is an example I´m testing with:

        var jsonText = ""
        let dictionary = ["firstName": "Björn", "lastName": "Tärnäby"] as [String : Any]
        if let theJSONData = try? JSONSerialization.data(
            withJSONObject: dictionary,
            options: []) {
            jsonText = String(data: theJSONData, encoding: .utf8)!
            print(jsonText)
        }

It prints out:

{"lastName":"Tärnäby","firstName":"Björn"}

What I would like to achieve is:

{"lastName":"T\u00e4rn\u00e4by","firstName":"Bj\u00f6rn"}

Is there an option in JSONSerialization or some other way to escape my strings in this way?