skip allow_superuser in Windows OS (#16629)

As user id is always zero in Windows,
this commit excluded the checking of running as root in Windows.

config/logstash.yml

@@ -320,7 +320,7 @@
 #
 # ------------ Other Settings --------------
 #
-# Allow or block running Logstash as superuser (default: true)
+# Allow or block running Logstash as superuser (default: true). Windows are excluded from the checking
 # allow_superuser: false
 #
 # Where to find custom plugins

logstash-core/lib/logstash/runner.rb

@@ -454,6 +454,8 @@ class LogStash::Runner < Clamp::StrictCommand
   end # def self.main
 
   def running_as_superuser
+    return if LogStash::Environment.windows? # windows euid always returns 0, skip checking
+
     if Process.euid() == 0
       if setting("allow_superuser")
         logger.warn("NOTICE: Allowing Logstash to run as superuser is heavily discouraged as it poses a security risk. " +

logstash-core/spec/logstash/runner_spec.rb

@@ -574,6 +574,15 @@ describe LogStash::Runner do
     let(:deprecation_logger_stub) { double("DeprecationLogger").as_null_object }
     before(:each) { allow(runner).to receive(:deprecation_logger).and_return(deprecation_logger_stub) }
 
+    if LogStash::Environment.windows?
+      context "unintentionally running logstash as superuser" do
+        it "runs successfully" do
+          LogStash::SETTINGS.set("allow_superuser", false)
+          expect(logger).not_to receive(:fatal)
+          expect { subject.run(args) }.not_to raise_error
+        end
+      end
+    else
       context "unintentionally running logstash as superuser" do
         before do
           expect(Process).to receive(:euid).and_return(0)
@@ -613,3 +622,4 @@ describe LogStash::Runner do
       end
     end
   end
+end