ASP.NET Core 2.0 JWT Validation fails with `Authorization failed for user: (null)` error

Question

I'm using ASP.NET Core 2.0 application (Web API) as a JWT issuer to generate a token consumable by a mobile app. Unfortunately, this token couldn't be validated by one controller while can be validated by another (using the same validation setting within the same asp.net core 2.0 app).

So I have a token which is valid and could be decoded, has all the required claims and timestamps. But one endpoint accepts it, while another gives me 401 error and debug output:

Microsoft.AspNetCore.Authorization.DefaultAuthorizationService:Information: Authorization failed for user: (null).

[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Authorization.DefaultAuthorizationService[2]
      Authorization failed for user: (null).
Microsoft.AspNetCore.Authorization.DefaultAuthorizationService:Information: Authorization failed for user: (null).
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[3]
      Authorization failed for the request at filter 'Microsoft.AspNetCore.Mvc.Authorization.AuthorizeFilter'.
Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Authorization failed for the request at filter 'Microsoft.AspNetCore.Mvc.Authorization.AuthorizeFilter'.
Microsoft.AspNetCore.Mvc.ChallengeResult:Information: Executing ChallengeResult with authentication schemes ().
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.ChallengeResult[1]
      Executing ChallengeResult with authentication schemes ().
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler[12]
      AuthenticationScheme: Bearer was challenged.
Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler:Information: AuthenticationScheme: Bearer was challenged.
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
      Executed action MyController.Get (WebApi) in 72.105ms
Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Executed action MyController.Get (WebApi) in 72.105ms
Microsoft.AspNetCore.Hosting.Internal.WebHost:Information: Request finished in 271.077ms 401 
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
      Request finished in 271.077ms 401 

My validation setup is below:

var secretKey = Configuration["Authentication:OAuth:IssuerSigningKey"];
var signingKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(secretKey));
var tokenValidationParameters = new TokenValidationParameters
{
   ValidateIssuerSigningKey = true,
   IssuerSigningKey = signingKey,
   ValidateIssuer = true,
   ValidIssuer = Configuration["Authentication:OAuth:Issuer"],
   ValidateAudience = true,
   ValidAudience = Configuration["Authentication:OAuth:Audience"],
   ValidateLifetime = true,
   ClockSkew = TimeSpan.Zero,
};

services.AddAuthentication(options =>
{
   options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
   options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
   options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
}).AddJwtBearer(options =>
{
    options.RequireHttpsMetadata = false;
    options.TokenValidationParameters = tokenValidationParameters;
});

These two endpoints are identical, just live in different controllers, both marked with the Authorize attribute.

How is that possible?

Answer 1

The sequence of the add statements in the configure function is of importance. Make sure that

app.UseAuthentication();

comes before

app.UseMvc();

Might this have been the problem?

Answer 2

In your startup.cs ConfigureServices method if you add

services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
            }).AddJwtBearer(options => ...

Explanation: When you use [Authorize] on a controller it binds to the first authorization system by default.

options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;

With this you are setting your default to JWT Bearer authentication.

additionally you can add

options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;

this line is how to prevent getting 404 not found errors when using Identity with JWTs. If you are using identity the DefaultChallengeScheme will try to redirect you to a login page, which if non existent will result in getting a 404 not found rather than the wanted 401 unauthorized. by setting the DefaultChallengeScheme to JwtBearerDefaults.AuthenticationScheme on unauthorized it will no longer try to redirect you to a login page

If you are using Cookie Authentication with JWT authentication in the [Authorize] tag you can specify what authenticationScheme you want. for example

[Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme)]

Answer 3

I added:

app.UseAuthentication();

In Startup.Configure() and that resolved this error for me.

Reference: Auth 2.0 Migration announcement

Answer 4

try this in startup.cs

services.AddAuthentication(options =>
        {
            options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
            options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
        }).AddJwtBearer(opts => ...

Answer 5

This seems to be the behavior you receive when your JWT isn't validated correctly. I had this problem as a result of typing "Bearer: (JWT)" instead of "Bearer (JWT)" in the header

Answer 6

When Authentications are added like:

  services.AddAuthentication(options => {
            options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
            options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
        })
        ....

It means that every attribute [Authorize] that is put on top of a method or a controller class, will try to authenticate against the default authentication schema (in this case the JwtBearer) AND IT WILL NOT CASCADE DOWN to try to authenticate with other schemas that might be declared (like Cookie schema). In order to make the AuthorizeAttribute authenticate against the cookie schema it has to be specified like

[Authorize(AuthenticationSchemes = CookieAuthenticationDefaults.AuthenticationScheme)]

This will work also the other way around, i.e. if cookie schema is default then the JwtBearer schema must be declared for authorization for those methods or controllers that would need JwtBearer token authentication

[Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme)]

Answer 7

Check signing key encoding in your token provider it can be for example UTF8 not ASCII.

Answer 8

You can try this instead:

.AddJwtBearer(options =>
{
    options.RequireHttpsMetadata = false;
    options.TokenValidationParameters = tokenValidationParameters;
});'