How to validate JWT Token in aspnet.core web api?

Question

I have created custom middleware class which validates the JWT token. I am calling this method before app.AddMvc() in configure method.

What should I add to Configuration services to authenticate my web API using JWT? I have added [Authorize] in my Controller class.

Do I need to call my middleware class which validates the JWT token first in Configure method? or I should call App.UseAuthentication() I am using the following order:

 app.UseAuthentication();
 app.MessageHandlerMiddleware();
 app.UseMvc();

I am new to .net web API implementation.

What's the reason for creating a "custom middleware class" for the JWT validation? Is there a specific reason you can't use the built-in validation process? — Kirk Larkin
– Kirk Larkin, Commented Aug 21, 2018 at 7:46
To be frank, I am not sure how to validate it using built in validation process!! Due to which I have created y own stuff for authentication — Girish
– Girish, Commented Aug 21, 2018 at 9:25
Have a read through Securing ASP.NET Core 2.0 Applications with JWTs and see if it helps. — Kirk Larkin
– Kirk Larkin, Commented Aug 21, 2018 at 11:15

Alex Herman · Accepted Answer · 2018-10-15 19:34:06Z

From one of my answers you can see how we pass JWT token and how the code looks for classic .NET (non-core) ASP.NET WebAPI 2.

There are not many differences, the code for ASP.NET Core looks similar.

The key aspect is - when you add JWT config in Startup the app handles validation automatically.

services
    .AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddJwtBearer(x =>
    {
        x.RequireHttpsMetadata = false;
        x.SaveToken = true;
        x.TokenValidationParameters = new TokenValidationParameters()
        {
            ValidateIssuerSigningKey = true,
            ValidateLifetime = true,
            IssuerSigningKey = _configuration.GetSymmetricSecurityKey(),
            ValidAudience = _configuration.GetValidAudience(),
            ValidIssuer = _configuration.GetValidIssuer()
        };
    });

(use the above link to see the implementation of GetSymmetricSecurityKey, GetValidAudience, GetValidIssuer ext. methods)

Also very important part:

services.AddAuthorization(auth =>
{
    auth
    .AddPolicy(
        _configuration.GetDefaultPolicy(),
        new AuthorizationPolicyBuilder()
            .AddAuthenticationSchemes(JwtBearerDefaults.AuthenticationScheme‌)
            .RequireAuthenticatedUser().Build()
    );
});

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