try to determine server uri better

src/web/Jordnaer/SignalR/AuthenticatedSignalRClientBase.cs

@@ -76,13 +76,30 @@ public async Task StopAsync(CancellationToken cancellationToken = default)
 
 	private CookieContainer? CreateCookieContainer(string cookie)
 	{
+		var allServerUris = _server.Features.Get<IServerAddressesFeature>()?.Addresses;
+		_logger.LogDebug("All server addresses: {@ServerAddresses}", allServerUris);
+
 		var serverUri = _server.Features.Get<IServerAddressesFeature>()?.Addresses.FirstOrDefault();
 		if (serverUri is null)
 		{
 			_logger.LogError("Failed to get server address from IServer");
 			return null;
 		}
 
+		if (serverUri.Contains("[::]"))
+		{
+			_logger.LogInformation(
+				"First server address was {ServerUri}, trying to get hostname from environment variable 'WEBSITE_HOSTNAME' instead.", serverUri);
+
+			serverUri = Environment.GetEnvironmentVariable("WEBSITE_HOSTNAME");
+		}
+
+		if (serverUri is null)
+		{
+			_logger.LogError("Cannot determine domain for Cookie, Environment.GetEnvironmentVariable(\"WEBSITE_HOSTNAME\") was null.");
+			return null;
+		}
+
 		var domain = new Uri(serverUri).Host;
 
 		var cookieContainer = new CookieContainer(1);
@@ -102,4 +119,4 @@ public async ValueTask DisposeAsync()
 
 		GC.SuppressFinalize(this);
 	}
-}
+}