Backport #13577

Disable auth gracefully without impacting existing watchers.

Signed-off-by: Lan Liang <gcslyp@gmail.com>

server/auth/store.go

@@ -1160,6 +1160,9 @@ func (as *authStore) AuthInfoFromTLS(ctx context.Context) (ai *AuthInfo) {
 }
 
 func (as *authStore) AuthInfoFromCtx(ctx context.Context) (*AuthInfo, error) {
+	if !as.IsAuthEnabled() {
+		return nil, nil
+	}
 	md, ok := metadata.FromIncomingContext(ctx)
 	if !ok {
 		return nil, nil