add validation for --oidc-issuer-url when using embedded OIDC

backend/options/oidc.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"strings"
 
 	"github.com/spf13/pflag"
 
@@ -130,6 +131,10 @@ func (options *OIDC) Validate() error {
 		return fmt.Errorf("invalid OIDC provider type: %s", options.Type)
 	}
 
+	if options.Type == string(kubebindv1alpha2.OIDCProviderTypeEmbedded) && !strings.HasSuffix(options.IssuerURL, "/oidc") {
+		return fmt.Errorf("--oidc-issuer-url must end with '/oidc' when using embedded OIDC provider")
+	}
+
 	if options.Type == string(kubebindv1alpha2.OIDCProviderTypeExternal) && len(options.AllowedGroups) == 0 && len(options.AllowedUsers) == 0 {
 		return fmt.Errorf("when using external OIDC provider, at least one of allowed groups or allowed users must be specified")
 	}

backend/options/oidc_test.go

@@ -0,0 +1,98 @@
+/*
+Copyright 2026 The Kube Bind Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package options
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	kubebindv1alpha2 "github.com/kube-bind/kube-bind/sdk/apis/kubebind/v1alpha2"
+)
+
+func TestOIDCValidate(t *testing.T) {
+	tests := []struct {
+		name    string
+		options *OIDC
+		wantErr bool
+		errMsg  string
+	}{
+		{
+			name: "embedded OIDC with valid issuer URL ending in /oidc",
+			options: &OIDC{
+				Type:               string(kubebindv1alpha2.OIDCProviderTypeEmbedded),
+				IssuerClientID:     "test-client-id",
+				IssuerClientSecret: "test-client-secret",
+				IssuerURL:          "http://localhost:8080/oidc",
+				CallbackURL:        "http://localhost:8080/callback",
+			},
+			wantErr: false,
+		},
+		{
+			name: "embedded OIDC with invalid issuer URL not ending in /oidc",
+			options: &OIDC{
+				Type:               string(kubebindv1alpha2.OIDCProviderTypeEmbedded),
+				IssuerClientID:     "test-client-id",
+				IssuerClientSecret: "test-client-secret",
+				IssuerURL:          "http://localhost:8080",
+				CallbackURL:        "http://localhost:8080/callback",
+			},
+			wantErr: true,
+			errMsg:  "--oidc-issuer-url must end with '/oidc' when using embedded OIDC provider",
+		},
+		{
+			name: "embedded OIDC with trailing slash /oidc/",
+			options: &OIDC{
+				Type:               string(kubebindv1alpha2.OIDCProviderTypeEmbedded),
+				IssuerClientID:     "test-client-id",
+				IssuerClientSecret: "test-client-secret",
+				IssuerURL:          "http://localhost:8080/oidc/",
+				CallbackURL:        "http://localhost:8080/callback",
+			},
+			wantErr: true,
+			errMsg:  "--oidc-issuer-url must end with '/oidc' when using embedded OIDC provider",
+		},
+		{
+			name: "external OIDC does not require /oidc suffix",
+			options: &OIDC{
+				Type:               string(kubebindv1alpha2.OIDCProviderTypeExternal),
+				IssuerClientID:     "test-client-id",
+				IssuerClientSecret: "test-client-secret",
+				IssuerURL:          "http://localhost:8080",
+				CallbackURL:        "http://localhost:8080/callback",
+				AllowedGroups:      []string{"admins"},
+			},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.options.Validate()
+
+			if !tt.wantErr {
+				require.NoError(t, err)
+				return
+			}
+
+			require.Error(t, err)
+			if tt.errMsg != "" {
+				require.EqualError(t, err, tt.errMsg)
+			}
+		})
+	}
+}