Asp.NET Identity 2 giving “Invalid Token” error

I encountered this problem and resolved it. There are several possible reasons.

1. URL-Encoding issues (if problem occurring “randomly”)

If this happens randomly, you might be running into url-encoding problems.
For unknown reasons, the token is not designed for url-safe, which means it might contain invalid characters when being passed through a url (for example, if sent via an e-mail).

In this case, HttpUtility.UrlEncode(token) and HttpUtility.UrlDecode(token) should be used.

As oão Pereira said in his comments, UrlDecode is not (or sometimes not?) required. Try both please. Thanks.

2. Non-matching methods (email vs password tokens)

For example:

    var code = await userManager.GenerateEmailConfirmationTokenAsync(user.Id);

and

    var result = await userManager.ResetPasswordAsync(user.Id, code, newPassword);

The token generated by the email-token-provide cannot be confirmed by the reset-password-token-provider.

But we will see the root cause of why this happens.

3. Different instances of token providers

Even if you are using:

var token = await _userManager.GeneratePasswordResetTokenAsync(user.Id);

along with

var result = await _userManager.ResetPasswordAsync(user.Id, HttpUtility.UrlDecode(token), newPassword);

the error still could happen.

My old code shows why:

public class AccountController : Controller
{
    private readonly UserManager _userManager = UserManager.CreateUserManager(); 

    [AllowAnonymous]
    [HttpPost]
    public async Task<ActionResult> ForgotPassword(FormCollection collection)
    {
        var token = await _userManager.GeneratePasswordResetTokenAsync(user.Id);
        var callbackUrl = Url.Action("ResetPassword", "Account", new { area = "", UserId = user.Id, token = HttpUtility.UrlEncode(token) }, Request.Url.Scheme);

        Mail.Send(...);
    }

and:

public class UserManager : UserManager<IdentityUser>
{
    private static readonly UserStore<IdentityUser> UserStore = new UserStore<IdentityUser>();
    private static readonly UserManager Instance = new UserManager();

    private UserManager()
        : base(UserStore)
    {
    }

    public static UserManager CreateUserManager()
    {
        var dataProtectionProvider = new DpapiDataProtectionProvider();
        Instance.UserTokenProvider = new DataProtectorTokenProvider<IdentityUser>(dataProtectionProvider.Create());

        return Instance;
    }

Pay attention that in this code, every time when a UserManager is created (or new-ed), a new dataProtectionProvider is generated as well. So when a user receives the email and clicks the link:

public class AccountController : Controller
{
    private readonly UserManager _userManager = UserManager.CreateUserManager();
    [HttpPost]
    [AllowAnonymous]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> ResetPassword(string userId, string token, FormCollection collection)
    {
        var result = await _userManager.ResetPasswordAsync(user.Id, HttpUtility.UrlDecode(token), newPassword);
        if (result != IdentityResult.Success)
            return Content(result.Errors.Aggregate("", (current, error) => current + error + "\r\n"));
        return RedirectToAction("Login");
    }

The AccountController is no longer the old one, and neither are the _userManager and its token provider. So the new token provider will fail because it has no that token in it’s memory.

Thus we need to use a single instance for the token provider. Here is my new code and it works fine:

public class UserManager : UserManager<IdentityUser>
{
    private static readonly UserStore<IdentityUser> UserStore = new UserStore<IdentityUser>();
    private static readonly UserManager Instance = new UserManager();

    private UserManager()
        : base(UserStore)
    {
    }

    public static UserManager CreateUserManager()
    {
        //...
        Instance.UserTokenProvider = TokenProvider.Provider;

        return Instance;
    }

and:

public static class TokenProvider
{
    [UsedImplicitly] private static DataProtectorTokenProvider<IdentityUser> _tokenProvider;

    public static DataProtectorTokenProvider<IdentityUser> Provider
    {
        get
        {

            if (_tokenProvider != null)
                return _tokenProvider;
            var dataProtectionProvider = new DpapiDataProtectionProvider();
            _tokenProvider = new DataProtectorTokenProvider<IdentityUser>(dataProtectionProvider.Create());
            return _tokenProvider;
        }
    }
}

It could not be called an elegant solution, but it hit the root and solved my problem.