diff --git a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-error-handlers.ts b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-error-handlers.ts
new file mode 100644
index 00000000000..76fe179b9f1
--- /dev/null
+++ b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-error-handlers.ts
@@ -0,0 +1,200 @@
+import { AxiosError } from "axios";
+
+import { BadRequestError, NotFoundError, UnauthorizedError } from "@app/lib/errors";
+
+type ErrorContext = {
+  host?: string;
+  port?: number;
+  kubernetesHost?: string;
+};
+
+export enum KubernetesAuthErrorContext {
+  KubernetesHost = "kubernetes-host",
+  KubernetesApiServer = "kubernetes-api-server",
+  GatewayProxy = "gateway-proxy"
+}
+
+type ErrorContextConfig = {
+  serviceName: string;
+  errorNamePrefix: string;
+  defaultErrorName: string;
+  default401Message: string;
+  default403Message: string;
+};
+
+const COMMON_KUBERNETES_MESSAGES = {
+  default401Message:
+    "Token reviewer JWT is invalid or expired. Please verify the token reviewer JWT is correct and has not expired.",
+  default403Message:
+    "Token reviewer JWT does not have permission to perform TokenReviews. Ensure the service account has the 'system:auth-delegator' ClusterRole binding."
+} as const;
+
+const ERROR_CONTEXT_CONFIGS: Record<KubernetesAuthErrorContext, ErrorContextConfig> = {
+  [KubernetesAuthErrorContext.KubernetesHost]: {
+    serviceName: "Kubernetes host",
+    errorNamePrefix: "KubernetesHost",
+    defaultErrorName: "KubernetesHostConnectionError",
+    ...COMMON_KUBERNETES_MESSAGES
+  },
+  [KubernetesAuthErrorContext.KubernetesApiServer]: {
+    serviceName: "Kubernetes API server",
+    errorNamePrefix: "Kubernetes",
+    defaultErrorName: "KubernetesConnectionError",
+    ...COMMON_KUBERNETES_MESSAGES
+  },
+  [KubernetesAuthErrorContext.GatewayProxy]: {
+    serviceName: "gateway proxy",
+    errorNamePrefix: "Gateway",
+    defaultErrorName: "GatewayConnectionError",
+    default401Message:
+      "Gateway service account is not authorized to perform TokenReviews. Verify the gateway has the 'system:auth-delegator' ClusterRole binding.",
+    default403Message:
+      "Gateway service account does not have permission to perform TokenReviews. Ensure it has the 'system:auth-delegator' ClusterRole binding."
+  }
+};
+
+/**
+ * Handles Axios network-level errors (connection refused, DNS failures, timeouts, etc.)
+ * Returns a BadRequestError with a descriptive message, or null if the error is not a network error.
+ */
+export const handleAxiosNetworkError = (
+  err: AxiosError,
+  context: ErrorContext,
+  contextType: KubernetesAuthErrorContext
+): BadRequestError | null => {
+  const { host, kubernetesHost } = context;
+  const target = host || kubernetesHost || "server";
+  const { errorNamePrefix: prefix, serviceName } = ERROR_CONTEXT_CONFIGS[contextType];
+
+  if (err.code === "ECONNREFUSED") {
+    return new BadRequestError({
+      name: `${prefix}ConnectionRefused`,
+      message: `Failed to connect to ${serviceName} at ${target}: Connection refused. Verify the host URL and ensure the ${serviceName.toLowerCase()} is accessible.`
+    });
+  }
+
+  if (err.code === "ENOTFOUND") {
+    return new BadRequestError({
+      name: `${prefix}HostNotFound`,
+      message: `Failed to resolve ${serviceName} hostname: ${target}. Verify the hostname is correct.`
+    });
+  }
+
+  if (err.code === "ETIMEDOUT" || err.code === "ECONNABORTED") {
+    return new BadRequestError({
+      name: `${prefix}ConnectionTimeout`,
+      message: `Connection to ${serviceName} at ${target} timed out. Verify network connectivity and firewall rules.`
+    });
+  }
+
+  if (err.code === "DEPTH_ZERO_SELF_SIGNED_CERT" || err.code === "SELF_SIGNED_CERT_IN_CHAIN") {
+    return new BadRequestError({
+      name: `${prefix}CertificateError`,
+      message: `SSL certificate verification failed for ${serviceName} at ${target}. The server uses a self-signed certificate. Please provide the CA certificate in the configuration.`
+    });
+  }
+
+  if (err.code === "UNABLE_TO_VERIFY_LEAF_SIGNATURE" || err.code === "CERT_HAS_EXPIRED") {
+    return new BadRequestError({
+      name: `${prefix}CertificateError`,
+      message: `SSL certificate verification failed for ${serviceName} at ${target}. Verify the CA certificate is correct and the server certificate is valid.`
+    });
+  }
+
+  return null;
+};
+
+/**
+ * Handles Axios HTTP response errors (401, 403, etc.)
+ * Returns an appropriate error, or null if not an HTTP error.
+ */
+export const handleAxiosHttpError = (
+  err: AxiosError,
+  contextType: KubernetesAuthErrorContext
+): UnauthorizedError | BadRequestError | null => {
+  if (!err.response) {
+    return null;
+  }
+
+  let message = (err.response.data as { message?: string })?.message;
+  const statusCode = err.response.status;
+  const { errorNamePrefix: prefix, default401Message, default403Message } = ERROR_CONTEXT_CONFIGS[contextType];
+
+  if (!message && typeof err.response.data === "string") {
+    message = err.response.data;
+  }
+
+  if (statusCode === 401) {
+    return new UnauthorizedError({
+      message: message || default401Message,
+      name: `${prefix}TokenReviewerUnauthorized`
+    });
+  }
+
+  if (statusCode === 403) {
+    return new UnauthorizedError({
+      message: message || default403Message,
+      name: `${prefix}TokenReviewerForbidden`
+    });
+  }
+
+  if (message) {
+    return new BadRequestError({
+      message,
+      name: `${prefix}TokenReviewRequestError`
+    });
+  }
+
+  // Generic HTTP error
+  return new BadRequestError({
+    name: `${prefix}TokenReviewRequestError`,
+    message: `${prefix} returned HTTP ${statusCode}: ${err.response.statusText || "Unknown error"}`
+  });
+};
+
+/**
+ * Handles generic Axios errors (fallback when network/HTTP handlers don't match)
+ */
+export const handleAxiosGenericError = (
+  err: AxiosError,
+  context: ErrorContext,
+  contextType: KubernetesAuthErrorContext
+): BadRequestError => {
+  const { host, kubernetesHost } = context;
+  const target = host || kubernetesHost || "server";
+  const { defaultErrorName, serviceName } = ERROR_CONTEXT_CONFIGS[contextType];
+
+  return new BadRequestError({
+    name: defaultErrorName,
+    message: `Failed to communicate with ${serviceName} at ${target}: ${err.message}`
+  });
+};
+
+/**
+ * Checks if an error is a known error type that should be re-thrown as-is.
+ */
+export const isKnownError = (err: unknown): boolean => {
+  return err instanceof UnauthorizedError || err instanceof BadRequestError || err instanceof NotFoundError;
+};
+
+/**
+ * Comprehensive Axios error handler that processes network, HTTP, and generic errors.
+ * Returns an error to throw.
+ */
+export const handleAxiosError = (
+  err: AxiosError,
+  context: ErrorContext,
+  contextType: KubernetesAuthErrorContext
+): BadRequestError | UnauthorizedError => {
+  const networkError = handleAxiosNetworkError(err, context, contextType);
+  if (networkError) {
+    return networkError;
+  }
+
+  const httpError = handleAxiosHttpError(err, contextType);
+  if (httpError) {
+    return httpError;
+  }
+
+  return handleAxiosGenericError(err, context, contextType);
+};
diff --git a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-fns.ts b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-fns.ts
index 194e69b3c37..e8404719682 100644
--- a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-fns.ts
+++ b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-fns.ts
@@ -1,3 +1,5 @@
+import { BadRequestError } from "@app/lib/errors";
+
 /**
  * Extracts the K8s service account name and namespace
  * from the username in this format: system:serviceaccount:default:infisical-auth
@@ -11,5 +13,8 @@ export const extractK8sUsername = (username: string) => {
       name: parts[3]
     };
   }
-  throw new Error("Invalid username format");
+  throw new BadRequestError({
+    name: "KubernetesUsernameParseError",
+    message: `Invalid Kubernetes service account username format: "${username}". Expected format: system:serviceaccount:<namespace>:<name>`
+  });
 };
diff --git a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-service.ts b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-service.ts
index 5d4021fef6c..f619436e7fb 100644
--- a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-service.ts
+++ b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-service.ts
@@ -1,6 +1,6 @@
 import { ForbiddenError, subject } from "@casl/ability";
 import { requestContext } from "@fastify/request-context";
-import axios, { AxiosError } from "axios";
+import axios, { AxiosError, AxiosRequestConfig, AxiosResponse } from "axios";
 import https from "https";
 import RE2 from "re2";
 
@@ -28,6 +28,7 @@ import {
 import { TPermissionServiceFactory } from "@app/ee/services/permission/permission-service-types";
 import { ProjectPermissionIdentityActions, ProjectPermissionSub } from "@app/ee/services/permission/project-permission";
 import { getConfig } from "@app/lib/config/env";
+import { request } from "@app/lib/config/request";
 import { crypto } from "@app/lib/crypto";
 import {
   BadRequestError,
@@ -52,6 +53,7 @@ import { TMembershipIdentityDALFactory } from "../membership-identity/membership
 import { TOrgDALFactory } from "../org/org-dal";
 import { validateIdentityUpdateForSuperAdminPrivileges } from "../super-admin/super-admin-fns";
 import { TIdentityKubernetesAuthDALFactory } from "./identity-kubernetes-auth-dal";
+import { handleAxiosError, isKnownError, KubernetesAuthErrorContext } from "./identity-kubernetes-auth-error-handlers";
 import { extractK8sUsername } from "./identity-kubernetes-auth-fns";
 import {
   IdentityKubernetesAuthTokenReviewMode,
@@ -62,6 +64,11 @@ import {
   TRevokeKubernetesAuthDTO,
   TUpdateKubernetesAuthDTO
 } from "./identity-kubernetes-auth-types";
+import {
+  GatewayRequestExecutor,
+  validateKubernetesHostConnectivity,
+  validateTokenReviewerPermissions
+} from "./identity-kubernetes-auth-validators";
 
 type TIdentityKubernetesAuthServiceFactoryDep = {
   identityDAL: Pick<TIdentityDALFactory, "findById">;
@@ -185,6 +192,70 @@ export const identityKubernetesAuthServiceFactory = ({
     return callbackResult;
   };
 
+  /**
+   * Supports two modes:
+   * - Gateway reviewer mode: Gateway uses its own service account (no kubernetesHost option)
+   * - API mode through gateway: Gateway proxies TCP connection to kubernetesHost (kubernetesHost option provided)
+   */
+  const $createGatewayValidationRequest = (
+    gatewayId: string,
+    options?: { kubernetesHost?: string; caCert?: string }
+  ): GatewayRequestExecutor => {
+    const useGatewayServiceAccount = !options?.kubernetesHost;
+
+    let targetHost: string | undefined;
+    let targetPort: number | undefined;
+    if (options?.kubernetesHost) {
+      const parsedUrl = new URL(options.kubernetesHost);
+      targetHost = parsedUrl.hostname;
+      targetPort = parsedUrl.port ? Number(parsedUrl.port) : 443;
+    }
+
+    return async <T>(method: "get" | "post", url: string, body?: object, headers?: Record<string, string>) => {
+      let response: AxiosResponse<T> | undefined;
+
+      await $gatewayProxyWrapper(
+        {
+          gatewayId,
+          reviewTokenThroughGateway: useGatewayServiceAccount,
+          targetHost,
+          targetPort,
+          caCert: options?.caCert
+        },
+        async (host: string, port: number, httpsAgent?: https.Agent) => {
+          const config: AxiosRequestConfig = {
+            headers: {
+              "Content-Type": "application/json",
+              ...(useGatewayServiceAccount
+                ? { "x-infisical-action": GatewayHttpProxyActions.UseGatewayK8sServiceAccount }
+                : headers)
+            },
+            timeout: 10000,
+            signal: AbortSignal.timeout(10000),
+            validateStatus: () => true,
+            ...(httpsAgent ? { httpsAgent } : {})
+          };
+
+          if (method === "get") {
+            response = await request.get<T>(`${host}:${port}${url}`, config);
+          } else {
+            response = await request.post<T>(`${host}:${port}${url}`, body, config);
+          }
+          return response.data;
+        }
+      );
+
+      if (!response) {
+        throw new BadRequestError({
+          name: "GatewayConnectionError",
+          message: "Failed to get response from gateway"
+        });
+      }
+
+      return response;
+    };
+  };
+
   const login = async ({ identityId, jwt: serviceAccountJwt, subOrganizationName }: TLoginKubernetesAuthDTO) => {
     const appCfg = getConfig();
     const identityKubernetesAuth = await identityKubernetesAuthDAL.findOne({ identityId });
@@ -276,28 +347,37 @@ export const identityKubernetesAuthServiceFactory = ({
           .catch((err) => {
             const tokenReviewerJwtSnippet = `${tokenReviewerJwt?.substring?.(0, 10) || ""}...${tokenReviewerJwt?.substring?.(tokenReviewerJwt.length - 10) || ""}`;
             const serviceAccountJwtSnippet = `${serviceAccountJwt?.substring?.(0, 10) || ""}...${serviceAccountJwt?.substring?.(serviceAccountJwt.length - 10) || ""}`;
+
             if (err instanceof AxiosError) {
               logger.error(
-                { response: err.response, host, port, tokenReviewerJwtSnippet, serviceAccountJwtSnippet },
+                {
+                  response: err.response,
+                  host,
+                  port,
+                  tokenReviewerJwtSnippet,
+                  serviceAccountJwtSnippet,
+                  code: err.code
+                },
                 "tokenReviewCallbackRaw: Kubernetes token review request error (request error)"
               );
-              if (err.response) {
-                const { message } = err?.response?.data as unknown as { message?: string };
-
-                if (message) {
-                  throw new UnauthorizedError({
-                    message,
-                    name: "KubernetesTokenReviewRequestError"
-                  });
-                }
-              }
-            } else {
-              logger.error(
-                { error: err as Error, host, port, tokenReviewerJwtSnippet, serviceAccountJwtSnippet },
-                "tokenReviewCallbackRaw: Kubernetes token review request error (non-request error)"
-              );
+
+              throw handleAxiosError(err, { host, port }, KubernetesAuthErrorContext.KubernetesApiServer);
+            }
+
+            logger.error(
+              { error: err as Error, host, port, tokenReviewerJwtSnippet, serviceAccountJwtSnippet },
+              "tokenReviewCallbackRaw: Kubernetes token review request error (non-request error)"
+            );
+
+            if (isKnownError(err)) {
+              throw err;
             }
-            throw err;
+
+            throw new BadRequestError({
+              name: "KubernetesTokenReviewError",
+              message: (err as Error).message || "Unexpected error during token review",
+              error: err
+            });
           });
 
         return res.data;
@@ -335,23 +415,24 @@ export const identityKubernetesAuthServiceFactory = ({
             }
           )
           .catch((err) => {
+            logger.error(
+              { error: err as Error, host, port },
+              "tokenReviewCallbackThroughGateway: Kubernetes token review request error"
+            );
+
             if (err instanceof AxiosError) {
-              if (err.response) {
-                let { message } = err?.response?.data as unknown as { message?: string };
-
-                if (!message && typeof err.response.data === "string") {
-                  message = err.response.data;
-                }
-
-                if (message) {
-                  throw new UnauthorizedError({
-                    message,
-                    name: "KubernetesTokenReviewRequestError"
-                  });
-                }
-              }
+              throw handleAxiosError(err, { host, port }, KubernetesAuthErrorContext.GatewayProxy);
+            }
+
+            if (isKnownError(err)) {
+              throw err;
             }
-            throw err;
+
+            throw new BadRequestError({
+              name: "GatewayTokenReviewError",
+              message: (err as Error).message || "Unexpected error during gateway token review",
+              error: err
+            });
           });
 
         return res.data;
@@ -571,7 +652,18 @@ export const identityKubernetesAuthServiceFactory = ({
           "user_agent.original": requestContext.get("userAgent")
         });
       }
-      throw error;
+
+      if (isKnownError(error)) {
+        throw error;
+      }
+
+      logger.error({ error, identityId }, "Unexpected error during Kubernetes auth login");
+
+      throw new BadRequestError({
+        name: "KubernetesAuthLoginError",
+        message: (error as Error).message || "An unexpected error occurred during Kubernetes authentication",
+        error
+      });
     }
   };
 
@@ -691,6 +783,39 @@ export const identityKubernetesAuthServiceFactory = ({
         OrgPermissionGatewayActions.AttachGateways,
         OrgPermissionSubjects.Gateway
       );
+
+      if (tokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Gateway) {
+        const gatewayExecutor = $createGatewayValidationRequest(gatewayId);
+        logger.info({ gatewayId }, "Validating gateway connectivity to Kubernetes");
+        await validateKubernetesHostConnectivity({ gatewayExecutor });
+        await validateTokenReviewerPermissions({ gatewayExecutor });
+      } else if (tokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Api && kubernetesHost) {
+        // API mode through gateway: gateway proxies requests with user's JWT
+        const gatewayExecutor = $createGatewayValidationRequest(gatewayId, {
+          kubernetesHost,
+          caCert: caCert || undefined
+        });
+        logger.info({ gatewayId, kubernetesHost }, "Validating Kubernetes connectivity through gateway");
+        await validateKubernetesHostConnectivity({ gatewayExecutor });
+        if (tokenReviewerJwt) {
+          await validateTokenReviewerPermissions({ gatewayExecutor, tokenReviewerJwt });
+        }
+      }
+    } else if (tokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Api && kubernetesHost) {
+      logger.info({ kubernetesHost }, "Validating Kubernetes host connectivity for new auth method");
+      await validateKubernetesHostConnectivity({
+        kubernetesHost,
+        caCert: caCert || undefined
+      });
+
+      if (tokenReviewerJwt) {
+        logger.info({ kubernetesHost }, "Validating token reviewer JWT permissions for new auth method");
+        await validateTokenReviewerPermissions({
+          kubernetesHost,
+          tokenReviewerJwt,
+          caCert: caCert || undefined
+        });
+      }
     }
 
     const { encryptor } = await kmsService.createCipherPairWithDataKey({
@@ -850,6 +975,75 @@ export const identityKubernetesAuthServiceFactory = ({
     const gatewayIdValue = isGatewayV1 ? gatewayId : null;
     const gatewayV2IdValue = isGatewayV1 ? null : gatewayId;
 
+    const effectiveTokenReviewMode = tokenReviewMode ?? identityKubernetesAuth.tokenReviewMode;
+    const effectiveKubernetesHost =
+      kubernetesHost !== undefined ? kubernetesHost : identityKubernetesAuth.kubernetesHost;
+    const effectiveGatewayId =
+      gatewayId !== undefined ? gatewayId : (identityKubernetesAuth.gatewayV2Id ?? identityKubernetesAuth.gatewayId);
+
+    const { encryptor, decryptor } = await kmsService.createCipherPairWithDataKey({
+      type: KmsDataKey.Organization,
+      orgId: identityMembershipOrg.scopeOrgId
+    });
+
+    let effectiveCaCert: string | undefined;
+    if (caCert !== undefined) {
+      effectiveCaCert = caCert;
+    } else if (identityKubernetesAuth.encryptedKubernetesCaCertificate) {
+      effectiveCaCert = decryptor({
+        cipherTextBlob: identityKubernetesAuth.encryptedKubernetesCaCertificate
+      }).toString();
+    } else {
+      effectiveCaCert = undefined;
+    }
+
+    if (effectiveGatewayId) {
+      if (effectiveTokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Gateway) {
+        const gatewayExecutor = $createGatewayValidationRequest(effectiveGatewayId);
+        logger.info(
+          { gatewayId: effectiveGatewayId },
+          "Validating gateway connectivity to Kubernetes for auth method update"
+        );
+
+        await validateKubernetesHostConnectivity({ gatewayExecutor });
+        await validateTokenReviewerPermissions({ gatewayExecutor });
+      } else if (effectiveTokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Api && effectiveKubernetesHost) {
+        const gatewayExecutor = $createGatewayValidationRequest(effectiveGatewayId, {
+          kubernetesHost: effectiveKubernetesHost,
+          caCert: effectiveCaCert
+        });
+        logger.info(
+          { gatewayId: effectiveGatewayId, kubernetesHost: effectiveKubernetesHost },
+          "Validating Kubernetes connectivity through gateway for auth method update"
+        );
+
+        await validateKubernetesHostConnectivity({ gatewayExecutor });
+        if (tokenReviewerJwt) {
+          await validateTokenReviewerPermissions({ gatewayExecutor, tokenReviewerJwt });
+        }
+      }
+    } else if (effectiveTokenReviewMode === IdentityKubernetesAuthTokenReviewMode.Api) {
+      if (kubernetesHost) {
+        logger.info({ kubernetesHost }, "Validating Kubernetes host connectivity for auth method update");
+        await validateKubernetesHostConnectivity({
+          kubernetesHost,
+          caCert: effectiveCaCert
+        });
+      }
+
+      if (tokenReviewerJwt && effectiveKubernetesHost) {
+        logger.info(
+          { kubernetesHost: effectiveKubernetesHost },
+          "Validating token reviewer JWT permissions for auth method update"
+        );
+        await validateTokenReviewerPermissions({
+          kubernetesHost: effectiveKubernetesHost,
+          tokenReviewerJwt,
+          caCert: effectiveCaCert
+        });
+      }
+    }
+
     const updateQuery: TIdentityKubernetesAuthsUpdate = {
       kubernetesHost,
       tokenReviewMode,
@@ -866,11 +1060,6 @@ export const identityKubernetesAuthServiceFactory = ({
         : undefined
     };
 
-    const { encryptor, decryptor } = await kmsService.createCipherPairWithDataKey({
-      type: KmsDataKey.Organization,
-      orgId: identityMembershipOrg.scopeOrgId
-    });
-
     if (caCert !== undefined) {
       updateQuery.encryptedKubernetesCaCertificate = encryptor({ plainText: Buffer.from(caCert) }).cipherTextBlob;
     }
diff --git a/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-validators.ts b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-validators.ts
new file mode 100644
index 00000000000..902c5b1b3b6
--- /dev/null
+++ b/backend/src/services/identity-kubernetes-auth/identity-kubernetes-auth-validators.ts
@@ -0,0 +1,229 @@
+import { AxiosError, AxiosResponse } from "axios";
+import https from "https";
+
+import { request } from "@app/lib/config/request";
+import { BadRequestError } from "@app/lib/errors";
+import { logger } from "@app/lib/logger";
+import { blockLocalAndPrivateIpAddresses } from "@app/lib/validator";
+
+import { handleAxiosError, KubernetesAuthErrorContext } from "./identity-kubernetes-auth-error-handlers";
+
+export type GatewayRequestExecutor = <T>(
+  method: "get" | "post",
+  url: string,
+  body?: object,
+  headers?: Record<string, string>
+) => Promise<AxiosResponse<T>>;
+
+/**
+ * Validates that the Kubernetes host is reachable by making a simple HTTPS request.
+ * This does not validate credentials, just network connectivity.
+ *
+ * Supports two modes:
+ * - API mode: Direct call to Kubernetes API (default)
+ * - Gateway mode: Call through gateway using gatewayExecutor
+ */
+export const validateKubernetesHostConnectivity = async ({
+  kubernetesHost,
+  caCert,
+  gatewayExecutor
+}: {
+  kubernetesHost?: string;
+  caCert?: string;
+  gatewayExecutor?: GatewayRequestExecutor;
+}): Promise<void> => {
+  const isGatewayMode = Boolean(gatewayExecutor);
+  const logContext = isGatewayMode ? { context: "gateway" } : { kubernetesHost };
+  const errorContext = isGatewayMode
+    ? KubernetesAuthErrorContext.GatewayProxy
+    : KubernetesAuthErrorContext.KubernetesHost;
+
+  try {
+    let response: AxiosResponse;
+
+    if (gatewayExecutor) {
+      response = await gatewayExecutor("get", "/version");
+    } else {
+      if (!kubernetesHost) {
+        throw new BadRequestError({
+          name: "KubernetesHostConnectionError",
+          message: "Kubernetes host is required for API mode validation"
+        });
+      }
+
+      const httpsAgent = new https.Agent({
+        ca: caCert || undefined,
+        rejectUnauthorized: Boolean(caCert)
+      });
+
+      await blockLocalAndPrivateIpAddresses(kubernetesHost);
+
+      response = await request.get(`${kubernetesHost}/version`, {
+        httpsAgent,
+        timeout: 10000,
+        signal: AbortSignal.timeout(10000),
+        validateStatus: () => true
+      });
+    }
+
+    if (response.status >= 500) {
+      throw new BadRequestError({
+        name: isGatewayMode ? "GatewayConnectionError" : "KubernetesHostConnectionError",
+        message: `Kubernetes API returned server error: ${response.status} - ${response.statusText}`
+      });
+    }
+
+    logger.info(logContext, "Kubernetes host connectivity validated successfully");
+  } catch (err) {
+    if (err instanceof BadRequestError) {
+      throw err;
+    }
+
+    const error = err as Error;
+    logger.error({ error, ...logContext }, "Failed to connect to Kubernetes host");
+
+    if (err instanceof AxiosError) {
+      throw handleAxiosError(err, { kubernetesHost }, errorContext);
+    }
+
+    throw new BadRequestError({
+      name: isGatewayMode ? "GatewayConnectionError" : "KubernetesHostConnectionError",
+      message: isGatewayMode
+        ? `Failed to connect to Kubernetes through gateway: ${error.message}`
+        : `Failed to connect to Kubernetes host at ${kubernetesHost}: ${error.message}`,
+      error
+    });
+  }
+};
+
+/**
+ * Validates that the token reviewer has the necessary permissions to perform token reviews.
+ * This is done by making a TokenReview request with a fake token to verify RBAC permissions
+ * without authenticating a real workload.
+ *
+ * Supports three modes:
+ * - API mode: Direct call to Kubernetes API using tokenReviewerJwt
+ * - Gateway mode (gateway reviewer): Gateway uses its own service account
+ * - Gateway mode (API reviewer): Gateway proxies request with user-provided tokenReviewerJwt
+ */
+export const validateTokenReviewerPermissions = async ({
+  kubernetesHost,
+  tokenReviewerJwt,
+  caCert,
+  gatewayExecutor
+}: {
+  kubernetesHost?: string;
+  tokenReviewerJwt?: string;
+  caCert?: string;
+  gatewayExecutor?: GatewayRequestExecutor;
+}): Promise<void> => {
+  const isGatewayMode = Boolean(gatewayExecutor);
+  const isGatewayWithUserJwt = isGatewayMode && Boolean(tokenReviewerJwt);
+  const logContext = isGatewayMode ? { context: "gateway" } : { kubernetesHost };
+  const errorContext = isGatewayMode
+    ? KubernetesAuthErrorContext.GatewayProxy
+    : KubernetesAuthErrorContext.KubernetesApiServer;
+
+  let errorNamePrefix = "TokenReviewer";
+  if (isGatewayMode && !isGatewayWithUserJwt) {
+    errorNamePrefix = "GatewayTokenReview";
+  }
+
+  try {
+    const testToken = "test-token-for-permission-validation";
+    const tokenReviewBody = {
+      apiVersion: "authentication.k8s.io/v1",
+      kind: "TokenReview",
+      spec: {
+        token: testToken
+      }
+    };
+
+    let response: AxiosResponse;
+
+    if (gatewayExecutor) {
+      // Gateway mode: optionally pass user JWT if provided (API mode through gateway)
+      const headers = tokenReviewerJwt ? { Authorization: `Bearer ${tokenReviewerJwt}` } : undefined;
+      response = await gatewayExecutor("post", "/apis/authentication.k8s.io/v1/tokenreviews", tokenReviewBody, headers);
+    } else {
+      // Direct API mode: call Kubernetes API directly
+      if (!kubernetesHost || !tokenReviewerJwt) {
+        throw new BadRequestError({
+          name: `${errorNamePrefix}PermissionError`,
+          message: "Kubernetes host and token reviewer JWT are required for API mode validation"
+        });
+      }
+
+      const httpsAgent = new https.Agent({
+        ca: caCert || undefined,
+        rejectUnauthorized: Boolean(caCert)
+      });
+
+      await blockLocalAndPrivateIpAddresses(kubernetesHost);
+
+      response = await request.post(`${kubernetesHost}/apis/authentication.k8s.io/v1/tokenreviews`, tokenReviewBody, {
+        headers: {
+          "Content-Type": "application/json",
+          Authorization: `Bearer ${tokenReviewerJwt}`
+        },
+        httpsAgent,
+        timeout: 10000,
+        signal: AbortSignal.timeout(10000),
+        validateStatus: () => true
+      });
+    }
+
+    if (response.status === 401) {
+      throw new BadRequestError({
+        name: `${errorNamePrefix}PermissionError`,
+        message:
+          isGatewayMode && !isGatewayWithUserJwt
+            ? "Gateway service account is not authorized. Verify the gateway is deployed correctly and has a valid service account."
+            : "The token reviewer JWT is invalid or expired. Please provide a valid service account token with TokenReview permissions."
+      });
+    }
+
+    if (response.status === 403) {
+      const errorMessage =
+        (response.data as { message?: string })?.message ||
+        (isGatewayMode && !isGatewayWithUserJwt
+          ? "Gateway service account does not have permission to perform TokenReviews."
+          : "The token reviewer JWT does not have permission to perform TokenReviews.");
+      throw new BadRequestError({
+        name: `${errorNamePrefix}PermissionError`,
+        message: `${errorMessage}. Ensure the service account has the 'system:auth-delegator' ClusterRole binding.`
+      });
+    }
+
+    if (response.status >= 200 && response.status < 300) {
+      const data = response.data as { status?: { authenticated?: boolean; error?: string } };
+      logger.info(
+        { ...logContext, authenticated: data?.status?.authenticated },
+        "Token reviewer permission validation successful"
+      );
+      return;
+    }
+
+    const errorMessage = (response.data as { message?: string })?.message || response.statusText;
+    throw new BadRequestError({
+      name: `${errorNamePrefix}PermissionError`,
+      message: `Unexpected response from Kubernetes API: ${response.status} - ${errorMessage}`
+    });
+  } catch (err) {
+    if (err instanceof BadRequestError) {
+      throw err;
+    }
+
+    const error = err as Error;
+    logger.error({ error, ...logContext }, "Failed to validate token reviewer permissions");
+
+    if (err instanceof AxiosError) {
+      throw handleAxiosError(err, { kubernetesHost }, errorContext);
+    }
+
+    throw new BadRequestError({
+      name: `${errorNamePrefix}PermissionError`,
+      message: `Failed to validate token reviewer permissions: ${error.message}`
+    });
+  }
+};