OutputCache but still going into code in Minimal API

Question

I am trying to get cache working on my API call but every time I do a request it goes straight into my lookup service code.

I have two services, stock and productlookup. The stock calls the productlookup to check to see if there is a product available for the stock.

To reduce the load on the lookup service I wanted to cache the requests to ease the load on the lookup service because the same request will be performed quite a few times. The problem is that even with the caching in place the code in the lookup is still being performed.

My setup code on my lookup service:

app.MapGet("/{ClientCode}/Stock/Lookup/{Sku}", Get)
   .WithApiVersionSet(vs)
   .Produces<LocationAdjustDto>(StatusCodes.Status200OK)
   .Produces<LocationAdjustDto>(StatusCodes.Status404NotFound)
   .WithSummary("Get Request.")
   .WithOpenApi()
   .MapToApiVersion(1)
   .CacheOutput();

public async Task<IResult> Get(IStockService stockService, IValidator<StockLookupRequest> validator, 
 [AsParameters] StockLookupRequest lookupRequest)
{}

My Program.cs file:

var builder = WebApplication.CreateBuilder(args);
builder.Configuration.AddEnvironmentVariables();
builder.Host.UseSerilog((context, configuration) =>     configuration.ReadFrom.Configuration(context.Configuration));
builder.Services.AddHealthChecks();
builder.Services.AddIdentityAuthentication(builder.Configuration, false);
builder.Services.AddUrlSegmentApiVersioning();
builder.Services.AddRepositories(builder.Configuration);
builder.Services.AddLookupService();
builder.Services.AddCarter();
builder.Services.AddOpenApi();
builder.Services.AddAuthorization();
builder.Services.AddOutputCache();

var app = builder.Build();

app.MapCarter();
app.UseOutputCache();
app.UseAuthorization();
app.Run();

We also do have a RequireAuthorization();.

Also calling the Lookup service using the GET request through Bruno doesn't work either.

James Andrew Smith · Accepted Answer · 2025-09-03 19:04:05Z

I found out the issue. It relates to the Authorization so it never caches. Adding a custom policy which I found somewhere else allows me to handle the authorization header.

code for reference

public class OutputCachePolicy : IOutputCachePolicy
{

    public static readonly OutputCachePolicy Instance = new();

    private OutputCachePolicy()
    {
    }

    ValueTask IOutputCachePolicy.CacheRequestAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        var attemptOutputCaching = AttemptOutputCaching(context);
        context.EnableOutputCaching = true;
        context.AllowCacheLookup = attemptOutputCaching;
        context.AllowCacheStorage = attemptOutputCaching;
        context.AllowLocking = true;

        // Vary by any query by default
        context.CacheVaryByRules.QueryKeys = "*";
        return ValueTask.CompletedTask;
    }
    // this never gets hit when Authorization is present
    ValueTask IOutputCachePolicy.ServeFromCacheAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        return ValueTask.CompletedTask;
    }

    ValueTask IOutputCachePolicy.ServeResponseAsync(OutputCacheContext context, CancellationToken cancellationToken)
    {
        var response = context.HttpContext.Response;
        context.AllowCacheStorage = true;

        return ValueTask.CompletedTask;
    }

    private static bool AttemptOutputCaching(OutputCacheContext context)
    {
        // Check if the current request fulfills the requirements to be cached

        var request = context.HttpContext.Request;

        // Verify the method
        if (!HttpMethods.IsGet(request.Method) && !HttpMethods.IsHead(request.Method))
        {
            return false;
        }

        // Verify existence of authorization headers
        //if (!StringValues.IsNullOrEmpty(request.Headers.Authorization) || request.HttpContext.User?.Identity?.IsAuthenticated == true)
        //{
        //    return false;
        //}
        return true;
    }

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