Is there something like sessions in dart? - session

Question

This may seem like a silly question but I am just starting out with dart and will need to verify user sesions similar to what you might do with PHP with the $_SESSION array...
So I am writing a basic server backend and a frontend and need to authenticate some requests that come in via XMLHttpRequest. The backend sends back JSON based on whether the given frontend is authenticated or not. In some cases, the frontend can update the DOM but only for the user who authenticated.
Not sure if I am explaining this well...
Any advice would be appreciated!!
Thanks!

Answer 1

A session is a high-level functionality that shouldn't be part of any language. You can include session functionality yourself by impelementing something like.
Map<String, int> sessions = {'abcdef12345' : 42}; // exists in e.g. datastore and is managed by an authentication routine
String authenticationToken = 'abcdef12345'; // comes from the request
if(sessions.containsKey(authenticationToken)) {
print('User ${sessions[authenticationToken]} is at least authenticated but might not have the appropriate rights to perform this operation.');
} else {
print('Not authenticated.');
}

Answer 2

Nothing like sessions is built in, but you can check out the recent Google API library for Dart to use oAuth:
Google API Dart Client

Answer 3

The package shelf_auth provides a nice full-automatic solution for session handing with its JwtSessionHandler implementation for shelf
var authMiddleware = authenticate([new RandomAuthenticator()],
new JwtSessionHandler('super app', 'shhh secret', testLookup));

Answer 4

Small example of using session with shelf package.
import 'dart:io' show Cookie;
import 'package:shelf/shelf.dart';
import 'package:shelf/shelf_io.dart' as io;
import 'package:shelf_router/shelf_router.dart';
import 'package:shelf_session/cookies_middleware.dart';
import 'package:shelf_session/session_middleware.dart';
import 'package:shelf_static/shelf_static.dart';
void main(List<String> args) async {
final router = Router();
router.get('/', _handleHome);
router.get('/login', _handleLogin);
router.get('/login/', _handleLogin);
router.post('/login', _handleLogin);
router.post('/login/', _handleLogin);
router.get('/logout', _handleLogout);
router.get('/logout/', _handleLogout);
final staticHandler =
createStaticHandler('web', defaultDocument: 'index.html');
final handler = Cascade().add(staticHandler).add(router).handler;
final pipeline = const Pipeline()
.addMiddleware(logRequests())
.addMiddleware(cookiesMiddleware())
.addMiddleware(sessionMiddleware())
.addHandler(handler);
const address = 'localhost';
const port = 8080;
final server = await io.serve(pipeline, address, port);
print('Serving at http://${server.address.host}:${server.port}');
}
const _menu = '''
Home<br />
Log in<br />
Log out<br />''';
Future<Response> _handleHome(Request request) async {
final userManager = UserManager();
final user = userManager.getUser(request);
var body = '$_menu{{message}}<br />{{cookies}}';
if (user == null) {
body = body.replaceAll('{{message}}', 'You are not logged in');
} else {
body = body.replaceAll('{{message}}', 'You are logged in as ${user.name}');
}
final cookies = request.getCookies();
body = body.replaceAll('{{cookies}}',
cookies.entries.map((e) => '${e.key}: ${e.value}').join('<br />'));
request.addCookie(Cookie('foo', 'Foo'));
if (!cookies.containsKey('baz')) {
request.addCookie(Cookie('baz', 'Baz'));
} else {
request.removeCookie(Cookie('baz', ''));
}
return _render(body);
}
Future<Response> _handleLogin(Request request) async {
const html = '''
<form action="" method="post">
<label>Login</label><br />
<input name="login" type="text" /><br />
<label>Password</label><br />
<input name="password" type="password" /><br /><br />
<button>Log in</button>
</form>
''';
if (request.method == 'GET') {
return _render(_menu + html);
}
final body = await request.readAsString();
final queryParameters = Uri(query: body).queryParameters;
final login = queryParameters['login'] ?? ''
..trim();
final password = queryParameters['password'] ?? ''
..trim();
if (login.isEmpty || password.isEmpty) {
return _render(_menu + html);
}
final user = User(login);
final userManager = UserManager();
userManager.setUser(request, user);
return Response.found('/');
}
Future<Response> _handleLogout(Request request) async {
Session.deleteSession(request);
return Response.found('/');
}
Response _render(String body) {
return Response.ok(body, headers: {
'Content-type': 'text/html; charset=UTF-8',
});
}
class User {
final String name;
User(this.name);
}
class UserManager {
User? getUser(Request request) {
final session = Session.getSession(request);
if (session == null) {
return null;
}
final user = session.data['user'];
if (user is User) {
return user;
}
return null;
}
User setUser(Request request, User user) {
var session = Session.getSession(request);
session ??= Session.createSession(request);
session.data['user'] = user;
return user;
}
}