Example Application Insights RequestTelemetry enhancement.

RequestTelemetryEnhancingMiddleware.cs

        public static IApplicationBuilder UseCorrelationProperties(this IApplicationBuilder app)
        {
            return app.Use(async (context, next) =>
                {
                    var logger = context.RequestServices.GetRequiredService<ILogger<CorrelationProperties>>();
                    
                    // NOTE: We're using Features and not RequestServices here.
					var requestTelemetry = context.Features.Get<RequestTelemetry>();
                    if (requestTelemetry != null)
                    {
                        // These show up in the customDimensions field
                        requestTelemetry.Context.Properties["Key1"] = "Value1";
                        requestTelemetry.Context.Properties["Key2"] = "Value2";
                    }
                    else
                    {
                        logger.LogWarning(
                            $"Could not retrieve {typeof(RequestTelemetry).FullName} from {typeof(HttpContext).FullName}. This could mean Application Insights is not running");
                    }

                    await next.Invoke();
                });
        }