Caching Claims in .net core 2.0

Question

Looked up everywhere but looks like I am stuck right now. I am using Windows Active Directory in my application for authentication. For authorization, I am using claims. After searching through the limited .net core documentation, this is how my code looks like.

Startup.cs

public void ConfigureServices(IServiceCollection services)
    {
        services.AddTransient<IPrincipal>(
            provider => provider.GetService<IHttpContextAccessor>().HttpContext.User);
        services.AddTransient<IClaimsTransformation, ClaimsTransformer>();
        services.AddAuthentication(IISDefaults.AuthenticationScheme);

    }

ClaimsTransformer.cs

class ClaimsTransformer : IClaimsTransformation
{
   public Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
   {

// call to database to get more claims based on user id ClaimsIdentity.Name
     ((ClaimsIdentity)principal.Identity).AddClaim(new Claim("now",DateTime.Now.ToString()));
     return Task.FromResult(principal);
   }
}

But the problem is, this code is called with every request and claims are loaded from the db every time which is absolutely wrong. Is there any way I can cache it? I was able to create a cookie of claims and use that cookie for any further calls in .net 4.0. I can't seem to find a way in the core. Any documentation I check, is incomplete or it does not cover my scenario. I am able to claims further in my application just how the documentation says here: https://docs.microsoft.com/en-us/aspnet/core/security/authorization/claims

But there is no mention about caching the claims.

Anyone in the same boat? Or knows the way out of it?

Answer 1

You can inject the IMemoryCache service in your ClaimsTransformer constructor.

using Microsoft.Extensions.Caching.Memory;

public class ClaimsTransformer : IClaimsTransformation
{
    private readonly IMemoryCache _cache;

    public ClaimsTransformer(IMemoryCache cache)
    {
        _cache = cache;
    }

    public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
    {
        var cacheKey = principal.FindFirstValue(ClaimTypes.NameIdentifier);

        if (_cache.TryGetValue(cacheKey, out List<Claim> claims)
        {
            ((ClaimsIdentity)principal.Identity).AddClaims(claims);
        }
        else
        {
            claims = new List<Claim>();          

            // call to database to get more claims based on user id ClaimsIdentity.Name

            _cache.Set(cacheKey, claims);
        }

        return principal;
    }
}