Custom AuthenticationHandler is called when a method has [AllowAnonymous]

Question

I am trying to have my own custom authentication for my server. But it is called for every endpoint even if it has the [AllowAnonymous] attribute on the method. With my current code, I can hit my breakpoint in the HandleAuthenticateAsync method everytime, even on the allow anonymous functions.

The AddCustomAuthentication adds the authenticationhandler correctly

        public void ConfigureServices(IServiceCollection services)
        {
            //services.AddAuthorization();
            services.AddAuthentication(options =>
            {
                // the scheme name has to match the value we're going to use in AuthenticationBuilder.AddScheme(...)
                options.DefaultAuthenticateScheme = "scheme";
                options.DefaultChallengeScheme = "scheme";
            })
            .AddCustomAuthentication(o => { });
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseAuthentication();

            app.UseMvc();
        }


...

    public class CustomAuthenticationHandler : AuthenticationHandler<CustomAuthenticationOptions>
    {

        public RvxAuthenticationHandler(
        IOptionsMonitor<RvxAuthenticationOptions> options,
        ILoggerFactory logger,
        UrlEncoder encoder,
        ISystemClock clock) : base(options, logger, encoder, clock)
        {
        }


        protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
        {
            var token = Request.Headers["token"].ToString();

            if (string.IsNullOrWhiteSpace(token))
            {
                return AuthenticateResult.Fail("Invalid Credentials");
            }


            return AuthenticateResult.Success(new AuthenticationTicket(new System.Security.Claims.ClaimsPrincipal(), "Hi"));
        }

Answer 1

Add this to the top of your HandleAuthenticateAsync method

protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        var endpoint = Context.GetEndpoint();
        if (endpoint?.Metadata?.GetMetadata<IAllowAnonymous>() != null)
        {
            return Task.FromResult(AuthenticateResult.NoResult());
        }

        ....
    }

This is what Microsoft use under the covers in the AuthorizeFiler - https://github.com/dotnet/aspnetcore/blob/bd65275148abc9b07a3b59797a88d485341152bf/src/Mvc/Mvc.Core/src/Authorization/AuthorizeFilter.cs#L236

It will allow you to use the AllowAnonymous attribute in controllers to bypass your custom AuthenticationHandler.