DART

Send Form Data in HTTP POST request in Flutter

import 'package:http/http.dart' as http;

void main() {
    // This will be sent as form data in the post requst
    var map = new Map<String, dynamic>();
    map['username'] = 'username';
    map['password'] = 'password';

    final response = await http.post(
        Uri.parse('http/url/of/your/api'),
        body: map,
    );

    print(response.body);
}

How to send post request using http in flutter

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:http/http.dart' as http;

Future<http.Response> postRequest () async {
  var url ='https://pae.ipportalegre.pt/testes2/wsjson/api/app/ws-authenticate';

  Map data = {
    'apikey': '12345678901234567890'
  }
  //encode Map to JSON
  var body = json.encode(data);

  var response = await http.post(url,
      headers: {"Content-Type": "application/json"},
      body: body
  );
  print("${response.statusCode}");
  print("${response.body}");
  return response;
}