Custom Authorize attribute - ASP .NET Core 2.2

Question

I want to create a custom Authorize attribute to be able to send a personalized response when it fails. There are many examples, but I could not find what I'm looking for. When registering a policy, I add a "claim". Is it possible to access that registered claim within the custom attribute without having to pass the claim by parameter? or is it possible to know if the check of the claim happened and if not, return a personalized response? Thx!

public static void AddCustomAuthorization(this IServiceCollection serviceCollection)
{
    serviceCollection.AddAuthorization(x =>
    {
        x.AddPolicy(UserPolicy.Read,
            currentPolicy => currentPolicy.RequireClaim(UserClaims.Read));
    });
}

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
public class CustomAuthorizeAttribute : AuthorizeAttribute, IAuthorizationFilter
{
    public void OnAuthorization(AuthorizationFilterContext authorizationFilterContext)
    {
        if (authorizationFilterContext.HttpContext.User.Identity.IsAuthenticated)
        {
            if (!authorizationFilterContext.HttpContext.User.HasClaim(x => x.Value == "CLAIM_NAME")) // ACCESS TO REGISTER CLAIM => currentPolicy => currentPolicy.RequireClaim(UserClaims.Read)
            {
                authorizationFilterContext.Result = new ObjectResult(new ApiResponse(HttpStatusCode.Unauthorized));
            }
        }
    }
}

[HttpGet]
[CustomAuthorizeAttribute(Policy = UserPolicy.Read)]
public async Task<IEnumerable<UserDTO>> Get()
{
    return ...
}

Answer 1

You can use IAuthorizationPolicyProvider to get the policy and then use ClaimsAuthorizationRequirement.ClaimType to get a claim name. And since it has async API, it is better to use IAsyncAuthorizationFilter instead of IAuthorizationFilter. Try this:

public class CustomAuthorizeAttribute : AuthorizeAttribute, IAsyncAuthorizationFilter
{
    public async Task OnAuthorizationAsync(AuthorizationFilterContext authorizationFilterContext)
    {
        var policyProvider = authorizationFilterContext.HttpContext
            .RequestServices.GetService<IAuthorizationPolicyProvider>();
        var policy = await policyProvider.GetPolicyAsync(UserPolicy.Read);
        var requirement = (ClaimsAuthorizationRequirement)policy.Requirements
            .First(r => r.GetType() == typeof(ClaimsAuthorizationRequirement));

        if (authorizationFilterContext.HttpContext.User.Identity.IsAuthenticated)
        {
            if (!authorizationFilterContext.HttpContext
              .User.HasClaim(x => x.Value == requirement.ClaimType))
            {
                authorizationFilterContext.Result = 
                   new ObjectResult(new ApiResponse(HttpStatusCode.Unauthorized));
            }
        }
    }
}

Answer 2

This attribute takes an array of strings, which was needed in my case. I needed to pass different users roles to this attribute and return result based on some custom logic.

public class CustomAuthFilter : AuthorizeAttribute, IAuthorizationFilter
{
    public CustomAuthFilter(params string[] args)
    {
        Args = args;
    }

    public string[] Args { get; }

    public void OnAuthorization(AuthorizationFilterContext context)
    {
        //Custom code ...

        //Resolving a custom Services from the container
        var service = context.HttpContext.RequestServices.GetRequiredService<ISample>();
        string name = service.GetName(); // returns "anish"

        //Return based on logic
        context.Result = new UnauthorizedResult();
    }
}

You can decorate your controller with this attribute as shown below

 [CustomAuthFilter("Anish","jiya","sample")]
 public async Task<IActionResult> Index()

Sample is a class that returns a hard coded string

public class Sample : ISample
{
    public string GetName() => "anish";
}

services.AddScoped(); //Register ISample, Sample as scoped.

FOR ASYNCHRONOUS SUPPORT use IAsyncAuthorizationFilter

public class CustomAuthFilter : AuthorizeAttribute, IAsyncAuthorizationFilter
{

    public CustomAuthFilter(params string[] args)
    {
        Args = args;
    }

    public string[] Args { get; }

    public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
    {
        //DO Whatever...

        //Resolve Services from the container
        var service = context.HttpContext.RequestServices.GetRequiredService<ISample>();
        var httpClientFactory = context.HttpContext.RequestServices.GetRequiredService<IHttpClientFactory>();
        string name = service.GetName();

        using var httpClient = httpClientFactory.CreateClient();

        var resp = await httpClient.GetAsync("https://jsonplaceholder.typicode.com/todos/1");
        var data = await resp.Content.ReadAsStringAsync();

        //Return based on logic
        context.Result = new UnauthorizedResult();

    }
}

Hope that helps..