ApplicationInsights request customDimensions - azure-application-insights

Question

Is it possible to add values to the customDimensions property of records in requests in ApplicationInsights? How?
I've found that logger.BeginScope can add them to traces -- the value must be Dictionary<string, object> (Passing Dictionary<string, string> does not work.)
Adding the properties to Activity.Current.AddTag has no effect.
Nor does adding properties to TelemetryClient.Properties.
(This is deprecated but nobody seems to know what to do instead.)

Answer 1

The answer is to use a custom ITelemetryInitializer like this
internal class TelemetryInitializer : ITelemetryInitializer
{
private static readonly string[] _Headers = new string[] { "Referer" /*sic */, "X-Forwarded-For", };
private readonly IHttpContextAccessor _httpContextAccessor;
public TelemetryInitializer(IHttpContextAccessor httpContextAccessor)
{
_httpContextAccessor = httpContextAccessor;
}
public void Initialize(ITelemetry item)
{
ISupportProperties tcp = item as ISupportProperties;
if (item == null || _httpContextAccessor.HttpContext == null) { return; }
LogTags tags = new LogTags();
tags.AddTag("BuildName", BuildNameAttribute.GetBuildName());
tags.AddTag("Method", _httpContextAccessor.HttpContext.Request.Method);
tags.AddTag("Host", _httpContextAccessor.HttpContext.Request.Host.Value);
// RequestPath is added automaticallt.
tags.AddTags(_httpContextAccessor.HttpContext.Request.Headers.Where(z => _Headers.Contains(z.Key)).SelectMany(z => z.Value.Select(y => new KeyValuePair<string, string>(z.Key, y))));
tags.AddTags(_httpContextAccessor.HttpContext.Request.Query.SelectMany(z => z.Value.Select(y => new KeyValuePair<string, string>(z.Key, y))));
if (_httpContextAccessor.HttpContext.Request.HasFormContentType && _httpContextAccessor.HttpContext.Request.Form != null)
{
tags.AddTags(_httpContextAccessor.HttpContext.Request.Form.Where(z => z.Key.ToLower().Contains("password")).SelectMany(z => z.Value.Select(y => new KeyValuePair<string, string>(z.Key, y.Length > 21 ? y.Substring(0, 21) + "..." : y))));
tags.AddTags(_httpContextAccessor.HttpContext.Request.Form.Files.Select(z => new KeyValuePair<string, string>("File", $"{z.ContentType} '{z.FileName}' {z.Length}")));
}
if (_httpContextAccessor.HttpContext.User.Identity?.IsAuthenticated ?? false)
{
tags.AddTags(_httpContextAccessor.HttpContext.User.Claims.Select(z => new KeyValuePair<string, string>(z.Type, z.Value)));
}
else
{
tags.AddTag("authentication", "none");
}
foreach (KeyValuePair<string, object> tag in tags.GetAllTags())
{
tcp.Properties[tag.Key] = tag.Value.ToString();
}
}
}
and
public static ILoggingBuilder AddLogging(this ILoggingBuilder builder, bool isDevelopment)
{
builder.ClearProviders();
Activity.DefaultIdFormat = ActivityIdFormat.W3C;
//builder.Services.AddApplicationInsightsTelemetry("key");
//Microsoft.ApplicationInsights.Extensibility.TelemetryConfiguration.Active.TelemetryChannel.DeveloperMode = true;
if (isDevelopment)
{
builder.AddBetterConsoleFormatter();
//builder.AddHttpRequestLogger(); // Just can't get this to work :(
//builder.AddBetterConsoleLogger(); // The singleton doesn't work very well and I don't understand why correlation IDs are omitted/
//builder.AddConsole();
builder.AddDebug();
}
else
{
// Add ApplicationInsights
builder.AddApplicationInsights();
builder.Services.AddApplicationInsightsTelemetry();
builder.Services.AddSingleton<ITelemetryInitializer, TelemetryInitializer>();
}
The IHttpContextAccessor deals with all that nastyness -- I was surprised to find that this is a singleton rather than scoped.
It turns out that this is not called until late on in the request pipeline which means that the auth middleware has run and therefore the .User is populated.