Jwt

• Jwt.Net, a JWT (JSON Web Token) implementation for .NET
• Sponsor
• Avaliable NuGet packages
• Supported .NET versions:
• Jwt.NET
  • Creating (encoding) token
    • Or using the fluent builder API
  • Parsing (decoding) and verifying token
    • Or using the fluent builder API
    • Or using the fluent builder API
  • Validate token expiration
  • Parsing (decoding) token header
    • Or using the fluent builder API
  • Turning off parts of token validation
    • Or using the fluent builder API
  • Custom JSON serializer
  • Custom JSON serialization settings with the default JsonNetSerializer
• Jwt.Net ASP.NET Core
  • Register authentication handler to validate JWT
  • Custom factories to produce Identity or AuthenticationTicket
• License

Jwt.Net, a JWT (JSON Web Token) implementation for .NET

This library supports generating and decoding JSON Web Tokens.

Sponsor

	If you want to quickly implement a secure authentication to your JWT project, create an Auth0 account; it's Free!

Avaliable NuGet packages

1. Jwt.Net

2. Jwt.Net for Microsoft Dependency Injection container

3. Jwt.Net for ASP.NET Core

Supported .NET versions:

• .NET Framework 3.5
• .NET Framework 4.0 - 4.8
• .NET Standard 1.3, 2.0
• .NET 6.0

Jwt.NET

Creating (encoding) token

var payload = new Dictionary<string, object>
{
    { "claim1", 0 },
    { "claim2", "claim2-value" }
};

IJwtAlgorithm algorithm = new RS256Algorithm(certificate);
IJsonSerializer serializer = new JsonNetSerializer();
IBase64UrlEncoder urlEncoder = new JwtBase64UrlEncoder();
IJwtEncoder encoder = new JwtEncoder(algorithm, serializer, urlEncoder);

var token = encoder.Encode(payload);
Console.WriteLine(token);

Or using the fluent builder API

var token = JwtBuilder.Create()
                      .WithAlgorithm(new RS256Algorithm(certificate))
                      .AddClaim("exp", DateTimeOffset.UtcNow.AddHours(1).ToUnixTimeSeconds())
                      .AddClaim("claim1", 0)
                      .AddClaim("claim2", "claim2-value")
                      .Encode();
Console.WriteLine(token);

Parsing (decoding) and verifying token

try
{
    IJsonSerializer serializer = new JsonNetSerializer();
    IDateTimeProvider provider = new UtcDateTimeProvider();
    IJwtValidator validator = new JwtValidator(serializer, provider);
    IBase64UrlEncoder urlEncoder = new JwtBase64UrlEncoder();
    IJwtAlgorithm algorithm = new RS256Algorithm(certificate);
    IJwtDecoder decoder = new JwtDecoder(serializer, validator, urlEncoder, algorithm);
    
    var json = decoder.Decode(token);
    Console.WriteLine(json);
}
catch (TokenNotYetValidException)
{
    Console.WriteLine("Token is not valid yet");
}
catch (TokenExpiredException)
{
    Console.WriteLine("Token has expired");
}
catch (SignatureVerificationException)
{
    Console.WriteLine("Token has invalid signature");
}

Or using the fluent builder API

var json = JwtBuilder.Create()
                     .WithAlgorithm(new RS256Algorithm(certificate))
                     .MustVerifySignature()
                     .Decode(token);                    
Console.WriteLine(json);

The output would be:

{ "claim1": 0, "claim2": "claim2-value" }

You can also deserialize the JSON payload directly to a .NET type:

var payload = decoder.DecodeToObject<IDictionary<string, object>>(token, secret);

Or using the fluent builder API

var payload = JwtBuilder.Create()
                        .WithAlgorithm(new RS256Algorithm(certificate))
                    .WithSecret(secret)
                        .MustVerifySignature()
                        .Decode<IDictionary<string, object>>(token);     

Validate token expiration

As described in the RFC 7519 section 4.1.4:

The exp claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing.

If it is present in the payload and is past the current time, the token will fail verification. The value must be specified as the number of seconds since the Unix epoch, 1/1/1970 00:00:00 UTC.

IDateTimeProvider provider = new UtcDateTimeProvider();
var now = provider.GetNow().AddMinutes(-5); // token has expired 5 minutes ago

double secondsSinceEpoch = UnixEpoch.GetSecondsSince(now);

var payload = new Dictionary<string, object>
{
    { "exp", secondsSinceEpoch }
};
var token = encoder.Encode(payload);

decoder.Decode(token); // throws TokenExpiredException

Then, as described in the RFC 7519 section 4.1.5:

The "nbf" (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing

If it is present in the payload and is prior to the current time, the token will fail verification.

Parsing (decoding) token header

IJsonSerializer serializer = new JsonNetSerializer();
IBase64UrlEncoder urlEncoder = new JwtBase64UrlEncoder();
IJwtDecoder decoder = new JwtDecoder(serializer, urlEncoder);

JwtHeader header = decoder.DecodeHeader<JwtHeader>(token);

var typ = header.Type; // JWT
var alg = header.Algorithm; // RS256
var kid = header.KeyId; // CFAEAE2D650A6CA9862575DE54371EA980643849

Or using the fluent builder API

JwtHeader header = JwtBuilder.Create()
                             .DecodeHeader<JwtHeader>(token);

var typ = header.Type; // JWT
var alg = header.Algorithm; // RS256
var kid = header.KeyId; // CFAEAE2D650A6CA9862575DE54371EA980643849

Turning off parts of token validation

If you'd like to validate a token but ignore certain parts of the validation (such as whether to the token has expired or not valid yet), you can pass a ValidateParameters object to the constructor of the JwtValidator class.

var validationParameters = new ValidationParameters
{
    ValidateSignature = true,
    ValidateExpirationTime = false,
    ValidateIssuedTime = false,
    TimeMargin = 100
};
IJwtValidator validator = new JwtValidator(serializer, provider, validationParameters);
IJwtDecoder decoder = new JwtDecoder(serializer, validator, urlEncoder, algorithm);
var json = decoder.Decode(expiredToken); // will not throw because of expired token

Or using the fluent builder API

var json = JwtBuilder.Create()
                     .WithAlgorithm(new RS256Algorirhm(certificate))
                     .WithSecret(secret)
                     .WithValidationParameters(
                         new ValidationParameters
                         {
                             ValidateSignature = true,
                             ValidateExpirationTime = false,
                             ValidateIssuedTime = false,
                             TimeMargin = 100
                         })
                     .Decode(expiredToken);

Custom JSON serializer

By default JSON serialization is performed by JsonNetSerializer implemented using Json.Net. To use a different one, implement the IJsonSerializer interface:

public sealed class CustomJsonSerializer : IJsonSerializer
{
    public string Serialize(object obj)
    {
        // Implement using favorite JSON serializer
    }

    public T Deserialize<T>(string json)
    {
        // Implement using favorite JSON serializer
    }
}

And then pass this serializer to JwtEncoder constructor:

IJwtAlgorithm algorithm = new RS256Algorirhm(certificate);
IJsonSerializer serializer = new CustomJsonSerializer();
IBase64UrlEncoder urlEncoder = new JwtBase64UrlEncoder();
IJwtEncoder encoder = new JwtEncoder(algorithm, serializer, urlEncoder);

Custom JSON serialization settings with the default JsonNetSerializer

As mentioned above, the default JSON serialization is done by JsonNetSerializer. You can define your own custom serialization settings as follows:

JsonSerializer customJsonSerializer = new JsonSerializer
{
    // All keys start with lowercase characters instead of the exact casing of the model/property, e.g. fullName
    ContractResolver = new CamelCasePropertyNamesContractResolver(), 
    
    // Nice and easy to read, but you can also use Formatting.None to reduce the payload size
    Formatting = Formatting.Indented,
    
    // The most appropriate datetime format.
    DateFormatHandling = DateFormatHandling.IsoDateFormat,
    
    // Don't add keys/values when the value is null.
    NullValueHandling = NullValueHandling.Ignore,
    
  // Use the enum string value, not the implicit int value, e.g. "red" for enum Color { Red }
    Converters.Add(new StringEnumConverter())
};
IJsonSerializer serializer = new JsonNetSerializer(customJsonSerializer);

Jwt.Net ASP.NET Core

Register authentication handler to validate JWT

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(options =>
                 {
                     options.DefaultAuthenticateScheme = JwtAuthenticationDefaults.AuthenticationScheme;
                     options.DefaultChallengeScheme = JwtAuthenticationDefaults.AuthenticationScheme;
                 })
            .AddJwt(options =>
                 {
                     // secrets, required only for symmetric algorithms, such as HMACSHA256Algorithm
                     // options.Keys = new[] { "mySecret" };
                     
                     // optionally; disable throwing an exception if JWT signature is invalid
                     // options.VerifySignature = false;
                 });
  // the non-generic version AddJwt() requires registering an instance of IAlgorithmFactory manually
  services.AddSingleton<IAlgorithmFactory>(new RSAlgorithmFactory(certificate));
  // or
  services.AddSingleton<IAlgorithmFactory>(new DelegateAlgorithmFactory(algorithm));

  // or use the generic version AddJwt<TFactory() to use a custom implementation of IAlgorithmFactory
  .AddJwt<MyCustomAlgorithmFactory>(options => ...);
}

public void Configure(IApplicationBuilder app)
{
    app.UseAuthentication();
}

Custom factories to produce Identity or AuthenticationTicket

services.AddSingleton<IIdentityFactory, CustomIdentityFctory>();
services.AddSingleton<ITicketFactory, CustomTicketFactory>();

License

The following projects and their resulting packages are licensed under Public Domain, see the LICENSE#Public-Domain file.

• JWT

The following projects and their resulting packages are licensed under the MIT License, see the LICENSE#MIT file.

• JWT.Extensions.AspNetCore
• JWT.Extensions.DependencyInjection