fix: ignore empty CA string in in-cluster OIDC config to prevent TLS parse error

Author: rayshoo

backend/pkg/kubeconfig/kubeconfig.go

@@ -983,7 +983,9 @@ func GetInClusterContext(oidcIssuerURL string,
 			IdpIssuerURL:  oidcIssuerURL,
 			Scopes:        strings.Split(oidcScopes, ","),
 			SkipTLSVerify: &oidcSkipTLSVerify,
-			CACert:        &oidcCACert,
+		}
+		if strings.TrimSpace(oidcCACert) != "" {
+			oidcConf.CACert = &oidcCACert
 		}
 	}