←

Let's create a URLRequest, set its method, and then specify it to be a urlencoded.

var r  = URLRequest(url: URL(string: u)!)
r.httpMethod = "POST"
r.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
let d = "somekey=someval&another=another".data(using:String.Encoding.ascii, allowLossyConversion: false)
r.httpBody = d

After we do that, we use the data method of the string to encode it as Data, and set the requests body as such. From that point we can use the request.

We'll use the URLSession's dataTask to create a task from all that.

let task = URLSession.shared.dataTask(with: r) { data, response, error in
  ...
}

Finall we call task.resume().