Which is the best way to validate current password? - asp.net

Question

I created a form where the user can update his data account. In this form the user is also able to change the account password, before doing so, I ask him the current password, this is the field:
<div class="form-group">
<label>Current Password</label>
<input class="form-control" id="oldPassword"
asp-for="#Model.ExistingPassword" type="password" />
<div class="invalid-feedback"></div>
</div>
as you can see the oldPassword input bound the property ExistingPassword which is part of the ViewModel of that View and have the following declaration:
[Required, MinLength(6), MaxLength(50), DataType(DataType.Password)]
public string ExistingPassword { get; set; }
when the form is submitted I call the following ajax function:
$.post(url, user, function (response) {
//Some stuff
}).done(function (response) {
alert("Updated executed");
}).fail(function (jqXHR, textStatus, errorThrown) {
alert("Error happened!");
});
the parameter of the function are taken by the form, in particular:
url: $(this).attr('action');
user: $(this).serialize();
the action of the form will call the following controller: User\UpdateUser.
Inside the UpdateUser method I execute the following check:
public async Task<UserProfileViewModel> UpdateUserAsync(UserProfileViewModel updatedUser)
{
if (!await _userManager.CheckPasswordAsync(originalUser, updatedUser.ExistingPassword))
throw new Exception("Invalid password");
essentially, the condition check if the current password is correct, if not, then an exception will raised.
Now, my question with this is: how can I know which type of exception the method has generated?
I need to know which type of exception the method UpdateUser has generated because there are different exceptions in the method.
Suppose the Invalid Password exceptions is raised, I need to display a message inside invalid-feedback div, next to oldPassword, so the user know why the update has failed.
Thanks in advance for any help.

Answer 1

Normally, I recommend not using an exception except in actual exception circumstances, but given the way you've designed this, you have a few options.
I'd suggest creating a custom "UpdateUserException" that you can throw that will include additional information, which can be provided by an enum or just string.
public class UpdateUserException : Exception {
public UpdateUserError ErrorCondition;
public UpdateUserException(UpdateUserError error, string message)
{
ErrorCondition = error;
Message = message;
}
}
then you would throw it
throw new UpdateUserException(UpdateUserError.BadPassword, "Invalid Password");
then you would catch it
try {}
catch (UpdateUserException e)
{
if (e.ErrorCondition == UpdateUserException.BadPassword)
{
// handle your exception.
}
}

Answer 2

Have a look at the UserManager ChangePassword Method.
You can bind the UserManager to use DependencyInjection like this (in Startup.cs)
public async void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
...
app.UseAuthentication();
app.UseMvc();
var scopeFactory = app.ApplicationServices.GetRequiredService<IServiceScopeFactory>();
using (var scope = scopeFactory.CreateScope())
{
UserManager<User> userManager = scope.ServiceProvider.GetRequiredService<UserManager<User>>();
}
}
And then in your Controller s Constructor
private readonly UserManager<User> _userManager;
public AccountController(UserManager<User> userManager)
{
_userManager = userManager;
}
And finally your endpoint:
[HttpPost("ChangePassword")]
public async Task<IActionResult> ChangePassword([FromBody]ChangePasswordRequest changePasswordParams)
{
if (changePasswordParams == null)
return BadRequest($"{nameof(changePasswordParams)} must not be null!");
if (string.IsNullOrWhiteSpace(changePasswordParams.OldPassword) || string.IsNullOrWhiteSpace(changePasswordParams.NewPassword))
return BadRequest("old and new passwords have to be provided, but they both are empty.");
var userId = User.Claims.FirstOrDefault(c => c.Type == "id")?.Value;
var user = await _userManager.FindByIdAsync(userId);
var result = await _userManager.ChangePasswordAsync(user, changePasswordParams.OldPassword, changePasswordParams.NewPassword);
if (result.Succeeded)
return NoContent();
return BadRequest(result.Errors);
}
after that you can handle the errors in a switch statement.

Answer 3

Using Exceptions for handled errors are not recommended since they generally ends up with Internal Server error and actually It is beyond of its purpose.
The best approach would be to send BadRequest as It is stated by #maerlin.
However, If you insist to use Exceptions in your application or your applciation is architected to work in this way. I suggest you to inherit new CustomApplcationException class from ApplicationException and then inherit UpdateUserException and vs. from CustomApplicationException class. After that, I Suggest you to handle your exceptions in ErrorHandlingMiddleware and return HandledExceptions at least with BadRequest (400) status code.
The Example Code would be
public class ExceptionMiddleware
{
private readonly RequestDelegate _next;
private readonly ILoggerManager _logger;
public ExceptionMiddleware(RequestDelegate next, ILoggerManager logger)
{
_logger = logger;
_next = next;
}
public async Task InvokeAsync(HttpContext httpContext)
{
try
{
await _next(httpContext);
}
catch (CustomApplicationException cae)
{
await HandleCustomExceptionAsync(httpContext, cae);
}
catch (Exception ex)
{
_logger.LogError($"Something went wrong: {ex}");
await HandleExceptionAsync(httpContext, ex);
}
}
private static Task HandleExceptionAsync(HttpContext context, Exception exception)
{
context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
return context.Response.WriteAsync(new ErrorDetails()
{
StatusCode = context.Response.StatusCode,
Message = "Internal Server Error from the custom middleware."
}.ToString());
}
private static Task HandleCustomExceptionAsync(HttpContext context, Exception exception)
{
context.Response.StatusCode = 400;
return context.Response.WriteAsync(new ErrorDetails()
{
StatusCode = context.Response.StatusCode,
Message = exception.Message
}.ToString());
}
}
then you need to regiter middleware in your Startup.cs
app.UseMiddleware<ExceptionMiddleware>();
please see https://code-maze.com/global-error-handling-aspnetcore/ and http://www.talkingdotnet.com/global-exception-handling-in-aspnet-core-webapi/ for further details.