JwtInspector - A Library for Decoding and Validating JWT Tokens

JwtInspector is a C# library that provides utilities for decoding, validating, and inspecting JWT (JSON Web Tokens). This library simplifies working with JWTs by providing easy-to-use methods for extracting data, validating tokens, and more.

The library supports various use cases, such as decoding JWT payloads, validating token expiration, and verifying the authenticity of tokens using HMAC-SHA algorithms.

Features

Decode JWT tokens to extract claims and payload.
Validate JWT token authenticity and expiration.
Support for handling iat (issued at), exp (expiration), and sub (subject) claims.
Provides a simple interface for inspecting JWT headers, payloads, and signatures.
Easy-to-use methods for handling base64 URL encoding and decoding.
JWT validation against a symmetric key (HMAC-SHA256) and token verification.

Installation

You can install the library via the NuGet package manager with the following command:

dotnet add package JwtInspector.Core

Usage

Decoding JWT Payload

To decode the payload of a JWT token and get a dictionary of claims:

using JwtInspector.Core.Services;

var jwtInspector = new JwtInspectorService();
string token = "<your-jwt-token>";
var claims = jwtInspector.DecodePayloadAsJson(token);
Console.WriteLine(claims);

Validating JWT Token

To validate a JWT token using a secret key:

using JwtInspector.Core.Services;

var jwtInspector = new JwtInspectorService();
string token = "<your-jwt-token>";
string secretKey = "<your-secret-key>";
bool isValid = jwtInspector.ValidateToken(token, secretKey);
Console.WriteLine($"Token valid: {isValid}");

Extracting JWT Parts

You can extract the header, payload, and signature from a JWT token:

using JwtInspector.Core.Services;

var jwtInspector = new JwtInspectorService();
string token = "<your-jwt-token>";
var (header, payload, signature) = jwtInspector.ExtractJwtParts(token);
Console.WriteLine($"Header: {header}");
Console.WriteLine($"Payload: {payload}");
Console.WriteLine($"Signature: {signature}");

Checking Token Expiration

To check if a JWT token is expired:

using JwtInspector.Core.Services;

var jwtInspector = new JwtInspectorService();
string token = "<your-jwt-token>";
bool isExpired = jwtInspector.IsExpired(token);
Console.WriteLine($"Token expired: {isExpired}");

Extracting JWT Claims

To get the claims from a JWT token:

using JwtInspector.Core.Services;

var jwtInspector = new JwtInspectorService();
string token = "<your-jwt-token>";
var claims = jwtInspector.GetClaims(token);
foreach (var claim in claims)
{
    Console.WriteLine($"{claim.Key}: {claim.Value}");
}

Example Usage: Validating a Token with HMAC-SHA256

using JwtInspector.Core.Services;
using Microsoft.IdentityModel.Tokens;

var jwtInspector = new JwtInspectorService();
string secretKey = "my_secret_key_123456789123456789"; // 32 bytes key
string token = "<your-jwt-token>";
bool isValid = jwtInspector.ValidateToken(token, secretKey);
Console.WriteLine($"Is token valid: {isValid}");

Methods Overview

Decoding methods

DecodeBase64Url(string input): Decodes a Base64Url encoded string.
DecodePayload(string token): Decodes the payload of a JWT token.
DecodePayloadAsJson(string token): Returns the decoded JWT payload as a JSON string.
ExtractJwtParts(string token): Extracts the header, payload, and signature from a JWT token.
GetAudience(string token): Extracts the audience (aud) from the JWT token.
GetClaims(string token): Extracts all claims from the JWT token.
GetExpirationDate(string token): Extracts the expiration date (exp) of the JWT token.
GetIssuedAt(string token): Extracts the issued date (iat) of the JWT token.
GetJwtId(string token): Extracts the JWT ID (jti) of the JWT token.
GetSigningAlgorithm(string token): Extracts the signing algorithm used in the JWT.
IsExpired(string token): Checks if the JWT token is expired.
IsValidFormat(string token): Checks if the JWT token has a valid format (three parts separated by dots).
GetIssuer(string token): Retrieves the issuer claim from the JWT token.
GetCustomClaim(string token, string claimKey): Retrieves a specific custom claim from the JWT token.
IDictionary<string, object> GetAllHeaders(string token): Retrieves all headers from the JWT token.
DecodePayloadAs<T>(string token): Deserializes the JWT payload into a strongly-typed object.
GetTokenSummary(string token): Generates a human-readable summary of the JWT token contents.

Validation methods

ValidateToken(string token, string secretKey): Validates the JWT token using the provided secret key for HMAC-SHA256 verification.
VerifyIssuer(string token, string expectedIssuer): Verifies that the issuer of the token matches the expected issuer.
ValidateIssuerAndAudience(string token, string expectedIssuer, string expectedAudience): Verifies that the issuer and audience of the token match the expected values.
ValidateLifetime(string token): Validates the token's lifetime based on the expiration date.
ValidateAlgorithm(string token, string expectedAlgorithm): Verifies that the algorithm used to sign the token matches the expected algorithm.
ValidateIssuerSigningKey(string token, string signingKey): Ensures that the token was signed using the correct signing key.
ValidateClaims(string token, IDictionary<string, string> requiredClaims): Validates specific claims in the token (e.g., roles, permissions).
ValidateNotBefore(string token): Validates that the token is not used before the specified 'Not Before' time (nbf claim).

JWT Format

A valid JWT token consists of three parts:

Header: Contains metadata such as the signing algorithm (alg) and token type (typ).
Payload: Contains the claims, which can be public, private, or registered claims such as sub, iat, exp, aud.
Signature: A cryptographic signature used to verify the integrity of the token.

A JWT token is typically represented in the following format: header.payload.signature

Example JWT

A typical JWT might look like this:

eyJhbGciOiAiSFMyNTYiLCAidHlwIjogIkpXVCJ9.eyJzdWIiOiAiMTIzNDU2Nzg5MCIsICJuYW1lIjogIkpvaG4gRG9lIiwgImlhdCI6IDE1MTYyMzkwMjJ9.MD8fpgF7N0XWhQGGVm9lA_EvVoHkcmrr74xhL2y7H3U

Contributing

Thank you for considering to help out with the source code! If you'd like to contribute, please fork, fix, commit and send a pull request for the maintainers to review and merge into the main code base.

Setting up Git
Fork the repository
Open an issue if you encounter a bug or have a suggestion for improvements/features

Licensee

JwtInspector source code is available under MIT License, see license in the source.

Contact

Please contact at francesco.delre.87[at]gmail.com for any details.

engineering87 / jwt-inspector