diff --git a/pkg/auth/iam/iam.go b/pkg/auth/iam/iam.go
index aa37d32..7fcc1db 100644
--- a/pkg/auth/iam/iam.go
+++ b/pkg/auth/iam/iam.go
@@ -300,25 +300,19 @@ func WithValidScope(scope string) FilterOption {
 // WithMatchedSubdomain filters request to a subdomain to match it with namespace in user's token
 func WithMatchedSubdomain(excludedNamespaces []string) FilterOption {
 	return func(req *restful.Request, iamClient iam.Client, claims *iam.JWTClaims) error {
-		parsedURL, err := url.Parse(req.Request.Host)
-		if err != nil {
-			// error parsing means the request comes from internal call, for example service to service call
-			return nil
-		}
-
-		part := strings.Split(parsedURL.Host, ".")
+		part := strings.Split(getHost(req.Request), ".")
 		if len(part) < 3 {
 			// url with subdomain should have at least 3 part, e.g. foo.example.com, otherwise we should not check it
 			return nil
 		}
 
 		for _, excludedNS := range excludedNamespaces {
-			if excludedNS == claims.Namespace {
+			if strings.ToLower(excludedNS) == strings.ToLower(claims.Namespace) {
 				return nil
 			}
 		}
 
-		if claims.Namespace == part[0] {
+		if strings.ToLower(claims.Namespace) == strings.ToLower(part[0]) {
 			return nil
 		}
 
@@ -327,6 +321,17 @@ func WithMatchedSubdomain(excludedNamespaces []string) FilterOption {
 	}
 }
 
+func getHost(req *http.Request) string {
+	if !req.URL.IsAbs() {
+		host := req.Host
+		if i := strings.Index(host, ":"); i != -1 {
+			host = host[:i]
+		}
+		return host
+	}
+	return req.URL.Host
+}
+
 // parseAccessToken is used to read token from Authorization Header or Cookie.
 // it will return the token value and token from.
 func parseAccessToken(request *restful.Request) (string, string, error) {
diff --git a/pkg/auth/iam/iam_test.go b/pkg/auth/iam/iam_test.go
index 358ef9b..b040384 100644
--- a/pkg/auth/iam/iam_test.go
+++ b/pkg/auth/iam/iam_test.go
@@ -16,6 +16,7 @@ package iam
 
 import (
 	"net/http"
+	"net/url"
 	"testing"
 
 	"github.com/AccelByte/go-restful-plugins/v4/pkg/constant"
@@ -161,3 +162,44 @@ func TestValidateRefererHeaderWithSubdomain(t *testing.T) {
 		})
 	}
 }
+
+// nolint:paralleltest
+func TestGetHost(t *testing.T) {
+	testcases := []struct {
+		name        string
+		expected    string
+		requestHost string
+		URLHost     string
+		scheme      string
+	}{
+		{
+			name:        "not_absolute_url",
+			requestHost: "host.example.com",
+			URLHost:     "url.example.com",
+			expected:    "host.example.com",
+		},
+		{
+			name:        "not_absolute_url_with_port",
+			requestHost: "host.example.com:80",
+			URLHost:     "url.example.com",
+			expected:    "host.example.com",
+		},
+		{
+			name:        "absolute_url_without_port",
+			requestHost: "host.example.com",
+			URLHost:     "url.example.com",
+			scheme:      "http",
+			expected:    "url.example.com",
+		},
+	}
+
+	for _, testcase := range testcases {
+		t.Run(testcase.name, func(t *testing.T) {
+			req := &http.Request{
+				Host: testcase.requestHost,
+				URL:  &url.URL{Host: testcase.URLHost, Scheme: testcase.scheme},
+			}
+			assert.Equal(t, testcase.expected, getHost(req))
+		})
+	}
+}