C# Get JWT Token from Request

#csharp #jwt #dotnet

This blog post will explore extracting a JWT token from incoming requests using C#.

We will explore two methods using Minimal APIs, but it's the same process for MVC Controllers.

JSON Web Tokens (JWT) have become famous for securing web applications and APIs. JWTs provide a way to transmit claims between parties securely and are widely used for authentication and authorization purposes.

Method 1: Parsing using Request Context
Method 2: Parsing directly from HTTP Headers
Conclusion

Method 1: Getting JWT from Authentication Context

This is the best way because it doesn't rely on the HTTP Headers. It uses the Authentication process instead.

PS.: The Authentication pipeline should be processed at this time.

using Microsoft.AspNetCore.Authentication;

app.MapGet("/jwt-token/context", async (HttpContext ctx) =>
{
    //get the access token from the HttpContext
    string token = await ctx.GetTokenAsync("access_token");

    return TypedResults.Ok(new { token = token });
});

Get Access Token from Authentication Context

Method 2: Parsing JWT Token from HTTP Headers

To retrieve the JWT token from a request, we need to access the request headers and extract the value of the "Authorization" header.

Here's a second example of how to parse the JWT token from a request:

app.MapGet("/jwt-token/headers", (HttpContext ctx) =>
{
    if (ctx.Request.Headers.TryGetValue("Authorization", out var headerAuth))
    {
        var jwtToken = headerAuth.First().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)[1];
        return Task.FromResult(
            TypedResults.Ok(new { token = jwtToken })
        );
    }
    return Task.FromResult(
        TypedResults.NotFound(new { message = "jwt not found" })
    );
});