Swift observable

auth.swift

import Foundation
import SwiftUI
import Combine

class HttpAuth: ObservableObject {

    @Published var authenticated = false

    func postAuth(username: String, password: String) {
        guard let url = URL(string: "http://mysite/login") else { return }

        let body: [String: String] = ["username": username, "password": password]

        let finalBody = try! JSONSerialization.data(withJSONObject: body)

        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.httpBody = finalBody
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")

        URLSession.shared.dataTask(with: request) { (data, response, error) in
            guard let data = data else { return }
            let resData = try! JSONDecoder().decode(ServerMessage.self, from: data)
            print(resData.res)
            if resData.res == "correct" {
                DispatchQueue.main.async {
                    self.authenticated = true
                }
            }
        }.resume()
    }
}

view.swift

import SwiftUI

struct ContentView: View {

    @State private var username: String = ""
    @State private var password: String = ""

    @ObservedObject var manager = HttpAuth()

    var body: some View {

        VStack(alignment: .leading) {

            if self.manager.authenticated {
                Text("Correct!").font(.headline)
            }

            Spacer()

            Text("Username")
            TextField("placeholder", text: $username)
                .textFieldStyle(RoundedBorderTextFieldStyle())
                .border(Color.green)
                .autocapitalization(.none)

            Text("Password")
            SecureField("placeholder", text: $password)
                .textFieldStyle(RoundedBorderTextFieldStyle())
                .border(Color.green)

            Button(action: {
                self.manager.postAuth(username: self.username, password: self.password)
            }) {
                HStack{
                    Spacer()
                    Text("Login")
                    Spacer()
                }
                .accentColor(Color.white)
                .padding(.vertical, 10)
                .background(Color.red)
                .cornerRadius(5)
                .padding(.horizontal, 40)

            }
            Spacer()
        }.padding()
    }

    struct ContentView_Previews: PreviewProvider {
        static var previews: some View {
            ContentView()
        }
    }
}