check user validation in Asp.net core with jwt authorization

Question

I implemented Microsoft Identity and JWT in my web api, a client can login and get a JWT token and store it in the application. since the expiration of the token the user can access the the server, but if I remove a user from my database, the removed user still has its token and can access the web api, how can I check the validation of the user?

Answer 1

One option is to validate the current user on the JwtBearerEvent OnTokenValidated event which will be triggered after every successful authentication

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

        options.Events = new JwtBearerEvents
            {
                OnTokenValidated = context =>
                {
                    var userService = ServiceProvider.GetService<IUserService>();
                    if(userService.IsUserRemoved(context.Principal.Identity.Name))
                        context.Fail("User is removed");

                    return Task.CompletedTask;
                }
            };
        });

Note: In this example I use ServiceProvider, to get the an instance of IUserService, which is stored in the Startup.cs class as a parameter. Initialized as ServiceProvider = services.BuildServiceProvider(); in the ConfigureServices method. The IUserService is a wrapper class where you need to implement the IsUserRemoved method which will operate on your user provider implementation.

Answer 2

Another option is to implement and register your own SecurityTokenValidator . To do so you need to create a class implemented ISecurityTokenValidator interface:

//using Microsoft.IdentityModel.Tokens

public class CustomValidator : ISecurityTokenValidator
{
   //interface implementation
   ...
}

and register it as an additional token validator via JwtBearerOptions.SecurityTokenValidators property :

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

        options.SecurityTokenValidators.Add(new CustomValidator()) 
    });