auth/oidc: fix eager token fetch at startup, add validation and e2e tests (#5234)

pkg/config/v1/validation/oidc.go

@@ -0,0 +1,57 @@
+// Copyright 2026 The frp 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 validation
+
+import (
+	"errors"
+	"net/url"
+	"strings"
+
+	v1 "github.com/fatedier/frp/pkg/config/v1"
+)
+
+func ValidateOIDCClientCredentialsConfig(c *v1.AuthOIDCClientConfig) error {
+	var errs []string
+
+	if c.ClientID == "" {
+		errs = append(errs, "auth.oidc.clientID is required")
+	}
+
+	if c.TokenEndpointURL == "" {
+		errs = append(errs, "auth.oidc.tokenEndpointURL is required")
+	} else {
+		tokenURL, err := url.Parse(c.TokenEndpointURL)
+		if err != nil || !tokenURL.IsAbs() || tokenURL.Host == "" {
+			errs = append(errs, "auth.oidc.tokenEndpointURL must be an absolute http or https URL")
+		} else if tokenURL.Scheme != "http" && tokenURL.Scheme != "https" {
+			errs = append(errs, "auth.oidc.tokenEndpointURL must use http or https")
+		}
+	}
+
+	if _, ok := c.AdditionalEndpointParams["scope"]; ok {
+		errs = append(errs, "auth.oidc.additionalEndpointParams.scope is not allowed; use auth.oidc.scope instead")
+	}
+
+	if c.Audience != "" {
+		if _, ok := c.AdditionalEndpointParams["audience"]; ok {
+			errs = append(errs, "cannot specify both auth.oidc.audience and auth.oidc.additionalEndpointParams.audience")
+		}
+	}
+
+	if len(errs) == 0 {
+		return nil
+	}
+	return errors.New(strings.Join(errs, "; "))
+}