Cache UserName and Domain to improve performance when creating new Ec…

…sDocument (#287)

Co-authored-by: Lightning Unicorn <lightning.unicorn.d@gmail.com>
Co-authored-by: Martijn Laarman <Mpdreamz@gmail.com>

src/Elastic.CommonSchema/EcsDocument.cs

@@ -57,9 +57,7 @@ public static TEcsDocument CreateNewWithDefaults<TEcsDocument>(
 
 		if (options?.IncludeHost is null or true) doc.Host = GetHost();
 		if (options?.IncludeProcess is null or true) doc.Process = GetProcess();
-		// TODO I think we can cache user? does CurrentPrincipal on Thread ever change?
-		if (options?.IncludeUser is null or true)
-			doc.User = new User { Id = Thread.CurrentPrincipal?.Identity.Name, Name = Environment.UserName, Domain = Environment.UserDomainName };
+		if (options?.IncludeUser is null or true) doc.User = GetUser();
 
 		return doc;
 	}
@@ -157,6 +155,12 @@ private static Process GetProcess()
 		};
 	}
 
+	private static readonly string UserName = Environment.UserName;
+	private static readonly string UserDomainName = Environment.UserDomainName;
+
+	//Can not cache current thread's identity as it's used for role based security, different threads can have different identities
+	private static User GetUser() => new User { Id = Thread.CurrentPrincipal?.Identity.Name, Name = UserName, Domain = UserDomainName };
+
 	private static Error GetError(Exception exception)
 	{
 		if (exception == null)