Introduction

When developing an ASP.NET Core 9 Web API that utilizes JWT (JSON Web Tokens) for authentication, handling token expiration correctly is crucial. Developers may encounter issues related to token expiration, especially when trying to test functionality that involves conditional time-based logic. In this article, we will explore a common error that users face regarding JWT expiration and how to effectively use a custom TimeProvider to facilitate testing.

Common JWT Token Expiration Issues

JWT tokens include claims relevant to the validity and lifetime of the token, which include Expires, NotBefore, and IssuedAt. When errors arise such as "Token is expired" or "Expires must be after NotBefore," this usually indicates that the token’s expiration has surpassed the current application's time, or there has been a misconfiguration in the time settings.

In the code snippets you provided, you are attempting to use a custom TimeProvider to ensure proper time control over token expiration, but running into errors. These errors arise primarily when the token creation logic does not synchronize with the testing environment’s expected time.

Understanding the Token Creation Process

Let’s take a look at how tokens are created in the TokenService:

Token Creation Method

Here’s the updated code you provided for creating a JWT using the TimeProvider:

public AccessTokenResponse CreateAccessToken(ApplicationUser user, string[] roles)
{
    List claims =
    [
        new(JwtRegisteredClaimNames.Sub, user.Id),
        new(JwtRegisteredClaimNames.Email, user.Email!),
        new(JwtRegisteredClaimNames.EmailVerified, user.EmailConfirmed.ToString()),
    ];

    claims.AddRange(roles.Select(role => new Claim(ClaimTypes.Role, role)));

    var signingKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtSettings.Secret));
    var credentials = new SigningCredentials(signingKey, SecurityAlgorithms.HmacSha512Signature);

    var now = timeProvider.GetUtcNow();
    var expiresAt = now.DateTime.AddMinutes(_jwtSettings.ExpiryInMinutes);

    var tokenDescriptor = new SecurityTokenDescriptor
    {
        Subject = new ClaimsIdentity(claims),
        Expires = expiresAt,
        SigningCredentials = credentials,
        Issuer = _jwtSettings.Issuer,
        Audience = _jwtSettings.Audience,
        NotBefore = now.DateTime,
        IssuedAt = now.DateTime,
    };

    var tokenHandler = new JwtSecurityTokenHandler();
    var token = tokenHandler.CreateToken(tokenDescriptor);
    return new AccessTokenResponse(tokenHandler.WriteToken(token), expiresAt);
}

Frequent Errors Encountered

  • "Bearer was not authenticated": This error indicates that the token created is being evaluated against a current time that exceeds its expiration time.
  • "Expires must be after NotBefore": This happens when the expiration date is mistakenly set to be before the NotBefore claim.

Setting Up the Custom TimeProvider in Tests

Testing token expiration logic often requires controlling the time environment accurately. Here, you have a custom FakeTimeProvider that should be injected into your service for tests. Let’s ensure it’s properly set up within the CustomWebApplicationFactory:

Custom Web Application Factory Example

Ensure that your factory removes and re-adds your TimeProvider effectively:

public class CustomWebApplicationFactory : WebApplicationFactory, IAsyncLifetime
{
    public readonly FakeTimeProvider FakeTimeProvider = new();

    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureTestServices(services =>
        {
            var timeProviderDescriptor = services.SingleOrDefault(d => d.ServiceType == typeof(TimeProvider));
            if (timeProviderDescriptor != null)
            {
                services.Remove(timeProviderDescriptor);
                services.AddSingleton(FakeTimeProvider);
            }
        });
    }
}

Tips on Testing with TimeProvider

  1. Initialize your FakeTimeProvider with specific dates. You can set it to a consistent starting point that aligns with your tests to avoid unpredictable results.
  2. Check for Singleton Registrations. Make sure your tests utilize the same instance of TimeProvider so there are no inconsistencies.
  3. Verify Time in Tests. Use assertions to validate that the current time utilized by your application (via FakeTimeProvider) matches your test expectations.

Frequently Asked Questions (FAQ)

What is JWT and how does it work in ASP.NET Core?

JWT, or JSON Web Token, is an open standard for securely transmitting information between parties. It encodes information in JSON, which is used in ASP.NET Core for authenticating users.

What are common errors related to JWT tokens?

Common errors include token expiration messages and validation failures. This usually indicates a mismatch between the token's time claims and the current test time or environment.

How can I test token expiration properly?

To properly test token expiration, ensure you have control over the time using a custom TimeProvider and thoroughly validate that token creation and validation align with your expectations in tests.

Conclusion

Handling token expiration logic within an ASP.NET Core API is an essential aspect of ensuring secure and reliable authentication. Utilizing a custom TimeProvider not only aids in testing scenarios but also promotes cleaner and more manageable code. Double-check your configurations and ensure that your testing environment properly reflects the time settings needed to avoid common JWT-related errors. By addressing token lifecycle management thoughtfully, you’ll streamline your application’s authentication process and resonate well with development best practices.