When working with Auth0 for authentication in a C# application, one common issue developers may encounter is the error message stating, "The provided redirect_uri is not in the list of allowed callback URLs." This error typically occurs when the redirect URI specified in your SignUp method does not match any of the allowed callback URLs configured in your Auth0 application settings.

Understanding the Redirect URI Issue

The redirect URI is a critical part of the OAuth 2.0 authentication flow that tells the authentication server where to send the user after they have successfully logged in or signed up. If this URI is not found in the list of allowed callback URLs in your Auth0 application settings, you will face the aforementioned error. The main takeaway here is that every redirect URI used in your application must be explicitly allowed in your Auth0 account.

Step-by-Step Solution

To resolve the redirect URI issue, you will need to:

Step 1: Verify the Redirect URI in Your C# Code

Ensure that the redirectUri specified in your SignUp method corresponds exactly to the URL you have allowed in your Auth0 settings. Update your SignUp method as follows:

public async Task SignUp(string returnUrl = "/")
{
    var redirectUri = Url.Action("CompleteProfile", "User"); // Generate URI
    var authenticationProperties = new LoginAuthenticationPropertiesBuilder()
        .WithRedirectUri(redirectUri)
        .WithParameter("screen_hint", "signup")
        .Build();

    await HttpContext.ChallengeAsync(Auth0Constants.AuthenticationScheme, authenticationProperties);
}

Step 2: Update Allowed Callback URLs in Auth0

Now, navigate to your Auth0 dashboard:

  1. Log in to your Auth0 account.
  2. Go to the Applications section and select your application.
  3. Locate the Allowed Callback URLs field.
  4. Add your redirect URI, which should look like: https://localhost:7106/User/CompleteProfile. Make sure there is no trailing slash or additional query strings unless required.
  5. Save your changes.

Step 3: Test the Redirect

After making the changes, make sure to test your SignUp functionality:

  1. Call the SignUp method.
  2. Complete the signup process and check if you are redirected to the CompleteProfile page without encountering any errors.

Handling CompleteProfile Method

Now, ensure that your CompleteProfile method in UserController is correctly implemented to handle both GET and POST requests:

GET Method

This method fetches the user information and checks whether the profile is complete or not:

[Authorize]
public async Task CompleteProfile()
{
    var auth0UserId = User.FindFirst(ClaimTypes.NameIdentifier)?.Value;
    var existingUser = await _context.Users.FirstOrDefaultAsync(u => u.Auth0UserId == auth0UserId);

    if (existingUser != null && existingUser.IsProfileComplete)
    {
        return RedirectToAction("Index", "Home");
    }
    return View(); // Show the profile completion form
}

POST Method

This method will handle the actual completion of user profiles:

[HttpPost]
[Authorize]
public async Task CompleteProfile(UsersViewModel model)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }

    var auth0UserId = User.FindFirst(ClaimTypes.NameIdentifier)?.Value;
    var email = User.FindFirst(ClaimTypes.Email)?.Value;

    var user = await _context.Users.FirstOrDefaultAsync(u => u.Auth0UserId == auth0UserId);

    if (user == null)
    {
        user = new Users
        {
            Auth0UserId = auth0UserId,
            Email = email,
            Name = model.Name,
            MobileContact = model.MobileContact,
            Address = model.Address,
            Gender = model.Gender,
            Birthday = model.Birthday,
            Role = "User",
            JoinDate = DateTime.Now,
            IsProfileComplete = true,
        };
        _context.Users.Add(user);
    }
    else
    {
        // Update entity properties
        user.Name = model.Name;
        user.MobileContact = model.MobileContact;
        user.Address = model.Address;
        user.Gender = model.Gender;
        user.Birthday = model.Birthday;
        user.IsProfileComplete = true;
    }
    await _context.SaveChangesAsync();

    return RedirectToAction("Index", "Home");
}

Frequently Asked Questions

What should I do if my redirect URI changes?

If you change your application's URL or the routing, ensure to update your Auth0 allowed callback URLs accordingly.

Can I use localhost URIs in production?

No, localhost URIs should only be used for development purposes. In production, always use your actual domain.

What if I encounter other Auth0 errors?

Check the Auth0 documentation for troubleshooting guides related to your specific error codes or messages.