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21:1526 | ViewData[`ReturnUrl`] = returnUrl; |
21:1527 | return View(); |
21:1528 | } |
21:1529 | |
21:1530 | It receives returnUrl as its parameter when the browser is automatically redirected to the login page by the authorization module. This happens when an unlogged-in user tries to access a protected page. returnUrl is stored in the ViewState dictionary that is passed to the login view. |
21:1531 | The form in the login view passes it back to the controller, together with the username and password when it is submitted, as shown in this code: |
21:1532 | <form asp-route-returnurl=`@ViewData[`ReturnUrl`]` method=`post`> |
21:1533 | ... |
21:1534 | </form> |
21:1535 | |
21:1536 | The form post is intercepted by an action method with the same Login name but decorated with the [HttpPost] attribute, as shown here: |
21:1537 | [ValidateAntiForgeryToken] |
21:1538 | public async Task<IActionResult> Login( |
21:1539 | LoginViewModel model, |
21:1540 | string? returnUrl = null) |
21:1541 | { |
21:1542 | ... |
21:1543 | |
21:1544 | The preceding method receives the Login model used by the login view, together with the returnUrl query string parameter. The ValidateAntiForgeryToken attribute verifies a token (called an anti-forgery token) that MVC forms automatically. This is then added to a hidden field to prevent XSRF/CSRF attacks. |
21:1545 | |
21:1546 | Forgery attacks exploit authentication cookies stored in the victim’s browser to submit a legitimate authenticated request to a web application. They do this by inducing the user to click a button on a phishing website that causes a submit to the target web application. The fraudulent request is accepted since, once a form is submitted, the authentication cookies for the target URL are automatically sent by the browser. There are just two defenses against this kind of attack: |
21:1547 | |
21:1548 | Authentication cookies are defined as same-origin – that is, they are sent from other domains just in case of GET requests. Thus, when a form is submitted from a phishing website to the target application, they are not sent. |
21:1549 | Anti-forgery tokens added to forms. In this case, if authentication cookies are sent together with the submitted form, the application understands that the request comes from a different website and blocks it since it is missing a valid anti-forgery token. |
21:1550 | |
21:1551 | |
21:1552 | As a first step, the action method logs the user out if they are already logged in: |
21:1553 | if (User.Identity.IsAuthenticated) |
21:1554 | { |
21:1555 | await signInManager.SignOutAsync(); |
21:1556 | |
21:1557 | } |
21:1558 | |
21:1559 | Otherwise, it verifies whether there are validation errors, in which case, it shows the same view filled with the data of the ViewModel to let the user correct their errors: |
21:1560 | if (ModelState.IsValid) |
21:1561 | { |
21:1562 | ... |
21:1563 | } |
21:1564 | else |
21:1565 | // If we got this far, something failed, redisplay form |
21:1566 | return View(model); |
21:1567 | |
21:1568 | If the model is valid, signInManager is used to log the user in: |
21:1569 | var result = await signInManager.PasswordSignInAsync( |
21:1570 | model.UserName, |
21:1571 | model.Password, model.RememberMe, |
21:1572 | lockoutOnFailure: false); |
21:1573 | |
21:1574 | If the result returned by the operation is successful, the action method redirects the browser to returnUrl if it’s not null; otherwise, it redirects the browser to the home page: |
21:1575 | if (result.Succeeded) |
21:1576 | { |
21:1577 | if (!string.IsNullOrEmpty(returnUrl)) |
21:1578 | return LocalRedirect(returnUrl); |
21:1579 | else |
21:1580 | return RedirectToAction(nameof(HomeController.Index), `Home`); |
21:1581 | } |
21:1582 | else |
21:1583 | { |
21:1584 | ModelState.AddModelError(string.Empty, |
21:1585 | `wrong username or password`); |
21:1586 | return View(model); |
21:1587 | } |
21:1588 | |
21:1589 | If the login fails, it adds an error to ModelState and shows the same form to let the user try again. |
21:1590 | ManagePackagesController contains an Index method that shows all packages in table format (for more details on controllers, views, and the MVC pattern in general, please refer to the The MVC pattern section of Chapter 17, Presenting ASP.NET Core): |
21:1591 | [HttpGet] |
21:1592 | public async Task<IActionResult> Index( |
21:1593 | [FromServices] IPackagesListQuery query) |
21:1594 | { |
21:1595 | var results = await query.GetAllPackages(); |
21:1596 | var vm = new PackagesListViewModel { Items = results }; |
21:1597 | return View(vm); |
21:1598 | } |
21:1599 | |
21:1600 | The query object is injected into the action method by DI. Then, the action method invokes it and inserts the resulting IEnumerable into the Items property of a PackagesListViewModel instance. It is a good practice to include IEnumerables in ViewModels instead of passing them directly to the views so that, if necessary, other properties can be added without the need to modify the existing view code. |
21:1601 | Moreover, it is good practice to define enumerable properties of ViewModels as IReadOnlyCollection<T> if the enumerables are read-only or as IList<T> if the enumerables can be modified or if they are involved in model binding. In fact, ICollection<T> has a Count property, which may be very useful when rendering ViewModels in views, while IList<T> also has indexers that are necessary for rendering all items with appropriate names for model binding to succeed (see this Phil Haack post: http://haacked.com/archive/2008/10/23/model-binding-to-a-list.aspx). IEnumerable<T> should be preferred only in the case that one needs the typical lazy evaluation of IEnumerable<T>. |
21:1602 | The results are shown in a Bootstrap table since Bootstrap CSS is automatically scaffolded by Visual Studio. Bootstrap is a good choice for a CSS framework, since it is quite simple and extensible, and is not connected to any particular company but is handled by an independent team. |
21:1603 | The result is shown here: |
21:1604 | |
21:1605 | Figure 21.29: Application packages handling page |
21:1606 | The New package link (it is shaped like a Bootstrap button, but it is a link) invokes a controller Create action method, while the delete and edit links in each row invoke a Delete and Edit action method, respectively, and pass them the ID of the package shown in the row. |
21:1607 | Here is the implementation of the two row links: |
21:1608 | @foreach(var package in Model.Items) |
21:1609 | { |
21:1610 | <tr> |
21:1611 | <td> |
21:1612 | <a asp-controller=`ManagePackages` |
21:1613 | asp-action=`@nameof(ManagePackagesController.Delete)` |
21:1614 | asp-route-id=`@package.Id`> |
21:1615 | delete |
21:1616 | </a> |
21:1617 | </td> |
21:1618 | <td> |
21:1619 | <a asp-controller=`ManagePackages` |
21:1620 | asp-action=`@nameof(ManagePackagesController.Edit)` |
21:1621 | asp-route-id=`@package.Id`> |
21:1622 | edit |
21:1623 | </a> |
21:1624 | </td> |
21:1625 | ... |
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