Integrate with ILogger{T}

[AKlaus]

Provide a way of logging non-OK responses via ILogger.
Have a way to automatically call ILogger.LogError() on returning NotFound, Failed, etc. Note: this option must be off by default, as the sad path of end-points execution usually leads to logging anyway.

Thought to add an option of manually logging on the call of ToActionResult (the ILogger needs to be added in the parameters), but that seems to be unnecessary. If there's a pressing need to log a custom message, a logger must be injected into the corresponding method of the service layer.

[AKlaus]

In case of an invalid ModelState, the official recommendation for logging is via leveraging ApiBehaviorOptions and described in dotnet/AspNetCore.Docs/issues/12157.

With a sample like this:

services.AddControllers()
    .ConfigureApiBehaviorOptions(options =>
    {
        // To preserve the default behavior, capture the original delegate to call later.
        var builtInFactory = options.InvalidModelStateResponseFactory;

        options.InvalidModelStateResponseFactory = context =>
        {
            var logger = context.HttpContext.RequestServices.GetRequiredService<ILogger<Startup>>();

            // Perform logging here.
            // ...

            // Invoke the default behavior, which produces a ValidationProblemDetails response.
            // To produce a custom response, return a different implementation of IActionResult instead.
            return builtInFactory(context);
        };
    });

Need to consider a similar approach for ToActionResult().

[AKlaus]

Another option is to implement a ProblemDetailsFactory (docs).

As an example, check out an implementation of that factory from khellang.