diff --git a/api/server/routes/admin/auth.js b/api/server/routes/admin/auth.js
index ee4af2a2b8..6c56e04938 100644
--- a/api/server/routes/admin/auth.js
+++ b/api/server/routes/admin/auth.js
@@ -41,46 +41,6 @@ const middleware = require('~/server/middleware');
 
 const requireAdminAccess = requireCapability(SystemCapabilities.ACCESS_ADMIN);
 
-function buildGoogleAdminRefreshDeps(sessionExpiry) {
-  return {
-    findUsers,
-    getUserById,
-    canAccessAdmin: async (user) => {
-      try {
-        return await hasCapability(
-          {
-            id: user.id ?? user._id?.toString(),
-            role: user.role ?? '',
-            tenantId: user.tenantId,
-          },
-          SystemCapabilities.ACCESS_ADMIN,
-        );
-      } catch (err) {
-        logger.warn(`[admin/oauth/refresh] capability check failed, denying: ${err?.message}`);
-        return false;
-      }
-    },
-    isEmailAllowed: async (user) => {
-      if (!user?.email) return false;
-      try {
-        const appConfig = user.tenantId
-          ? await resolveAppConfigForUser(getAppConfig, user)
-          : await getAppConfig({ baseOnly: true });
-        return isEmailDomainAllowed(user.email, appConfig?.registration?.allowedDomains);
-      } catch (err) {
-        logger.warn(
-          `[admin/oauth/refresh] domain allowlist check failed, denying: ${err?.message}`,
-        );
-        return false;
-      }
-    },
-    mintToken: async (user) => ({
-      token: await generateToken(user, sessionExpiry),
-      expiresAt: Date.now() + sessionExpiry,
-    }),
-  };
-}
-
 const setBalanceConfig = createSetBalanceConfig({
   getAppConfig,
   findBalanceByUser,
@@ -111,6 +71,52 @@ function resolveRequestOrigin(req) {
   }
 }
 
+function buildAdminRefreshClosures(sessionExpiry) {
+  return {
+    canAccessAdmin: async (user) => {
+      try {
+        return await hasCapability(
+          {
+            id: user.id ?? user._id?.toString(),
+            role: user.role ?? '',
+            tenantId: user.tenantId,
+          },
+          SystemCapabilities.ACCESS_ADMIN,
+        );
+      } catch (err) {
+        logger.warn(`[admin/oauth/refresh] capability check failed, denying: ${err?.message}`);
+        return false;
+      }
+    },
+    mintToken: async (user) => ({
+      token: await generateToken(user, sessionExpiry),
+      expiresAt: Date.now() + sessionExpiry,
+    }),
+  };
+}
+
+function buildGoogleAdminRefreshDeps(sessionExpiry) {
+  return {
+    findUsers,
+    getUserById,
+    ...buildAdminRefreshClosures(sessionExpiry),
+    isEmailAllowed: async (user) => {
+      if (!user?.email) return false;
+      try {
+        const appConfig = user.tenantId
+          ? await resolveAppConfigForUser(getAppConfig, user)
+          : await getAppConfig({ baseOnly: true });
+        return isEmailDomainAllowed(user.email, appConfig?.registration?.allowedDomains);
+      } catch (err) {
+        logger.warn(
+          `[admin/oauth/refresh] domain allowlist check failed, denying: ${err?.message}`,
+        );
+        return false;
+      }
+    },
+  };
+}
+
 router.post(
   '/login/local',
   middleware.logHeaders,
@@ -654,27 +660,7 @@ router.post(
           {
             findUsers,
             getUserById,
-            canAccessAdmin: async (user) => {
-              try {
-                return await hasCapability(
-                  {
-                    id: user.id ?? user._id?.toString(),
-                    role: user.role ?? '',
-                    tenantId: user.tenantId,
-                  },
-                  SystemCapabilities.ACCESS_ADMIN,
-                );
-              } catch (err) {
-                logger.warn(
-                  `[admin/oauth/refresh] capability check failed, denying: ${err?.message}`,
-                );
-                return false;
-              }
-            },
-            mintToken: async (user) => ({
-              token: await generateToken(user, sessionExpiry),
-              expiresAt: Date.now() + sessionExpiry,
-            }),
+            ...buildAdminRefreshClosures(sessionExpiry),
           },
           {
             userId: normalizedUserId,
diff --git a/api/server/routes/admin/auth.refresh.test.js b/api/server/routes/admin/auth.refresh.test.js
index b9a2c7b68c..72eaede651 100644
--- a/api/server/routes/admin/auth.refresh.test.js
+++ b/api/server/routes/admin/auth.refresh.test.js
@@ -296,7 +296,15 @@ describe('admin auth Google refresh route', () => {
     expect(response.body).toEqual({
       token: 'admin-jwt',
       refreshToken: 'rotated-refresh',
-      user: expect.objectContaining({ provider: 'google' }),
+      user: expect.objectContaining({
+        _id: 'user-id',
+        id: 'user-id',
+        email: 'admin@example.com',
+        name: 'Admin',
+        username: 'admin',
+        role: 'ADMIN',
+        provider: 'google',
+      }),
       expiresAt: 1234567890,
     });
     expect(applyGoogleAdminRefresh).toHaveBeenCalledWith(
@@ -316,6 +324,45 @@ describe('admin auth Google refresh route', () => {
     );
   });
 
+  it('forwards the tenant id from getTenantId() to the helper', async () => {
+    const { getTenantId } = require('@librechat/data-schemas');
+    getTenantId.mockReturnValueOnce('tenant-x');
+
+    const response = await request(app)
+      .post('/api/admin/oauth/refresh')
+      .send({ refresh_token: 'incoming-google-refresh', provider: 'google' });
+
+    expect(response.status).toBe(200);
+    expect(applyGoogleAdminRefresh).toHaveBeenCalledWith(
+      expect.any(Object),
+      expect.objectContaining({ tenantId: 'tenant-x' }),
+    );
+  });
+
+  it('canAccessAdmin closure calls hasCapability with the normalized user id', async () => {
+    const { hasCapability } = require('~/server/middleware/roles/capabilities');
+    let capturedDeps;
+    applyGoogleAdminRefresh.mockImplementationOnce(async (deps) => {
+      capturedDeps = deps;
+      return {
+        token: 'jwt',
+        refreshToken: 'r',
+        user: { id: 'u', _id: 'u', email: 'e@e.com', name: '', username: '', role: 'ADMIN' },
+        expiresAt: 0,
+      };
+    });
+
+    await request(app)
+      .post('/api/admin/oauth/refresh')
+      .send({ refresh_token: 'google-refresh', provider: 'google' });
+
+    await capturedDeps.canAccessAdmin({ id: 'user-1', role: 'ADMIN', tenantId: 'tenant-a' });
+    expect(hasCapability).toHaveBeenCalledWith(
+      { id: 'user-1', role: 'ADMIN', tenantId: 'tenant-a' },
+      'ACCESS_ADMIN',
+    );
+  });
+
   it('does not require OPENID_REUSE_TOKENS for the google provider', async () => {
     isEnabled.mockReturnValue(false);
 
diff --git a/api/strategies/socialLogin.js b/api/strategies/socialLogin.js
index cf86eebb81..459e69e47d 100644
--- a/api/strategies/socialLogin.js
+++ b/api/strategies/socialLogin.js
@@ -56,7 +56,7 @@ const socialLogin =
       }
 
       const passResult = (user) =>
-        refreshToken ? cb(null, user, { refreshToken }) : cb(null, user);
+        refreshToken && provider === 'google' ? cb(null, user, { refreshToken }) : cb(null, user);
 
       if (existingUser?.provider === provider) {
         if (
@@ -74,6 +74,15 @@ const socialLogin =
         }
         if (options.existingUsersOnly && id && !existingUser[providerKey]) {
           await updateUser(existingUser._id, { [providerKey]: id });
+          const verified = await findUser({ _id: existingUser._id, [providerKey]: id });
+          if (!verified) {
+            logger.warn(
+              `[${provider}Login] Admin migrate superseded by concurrent write, denying: ${email}`,
+            );
+            const concurrentError = new Error(ErrorTypes.AUTH_FAILED);
+            concurrentError.code = ErrorTypes.AUTH_FAILED;
+            return cb(concurrentError);
+          }
           existingUser[providerKey] = id;
         }
         await handleExistingUser(existingUser, avatarUrl, appConfig, email);
diff --git a/api/strategies/socialLogin.test.js b/api/strategies/socialLogin.test.js
index 14f2ae1f20..0ea950cc80 100644
--- a/api/strategies/socialLogin.test.js
+++ b/api/strategies/socialLogin.test.js
@@ -177,6 +177,37 @@ describe('socialLogin', () => {
       expect(callback).toHaveBeenCalledWith(null, existingUser);
     });
 
+    it('does not migrate the provider id on the chat path (only admin path migrates)', async () => {
+      const { updateUser } = require('~/models');
+      const provider = 'google';
+      const googleId = 'google-user-chat';
+      const email = 'chat@example.com';
+
+      const existingUser = {
+        _id: 'chatUser',
+        email: email,
+        provider: 'google',
+      };
+
+      findUser.mockResolvedValueOnce(null).mockResolvedValueOnce(existingUser);
+
+      const mockProfile = {
+        id: googleId,
+        emails: [{ value: email, verified: true }],
+        photos: [{ value: 'https://example.com/avatar.png' }],
+        name: { givenName: 'Chat', familyName: 'User' },
+      };
+
+      const loginFn = socialLogin(provider, mockGetProfileDetails);
+      const callback = jest.fn();
+
+      await loginFn(null, null, null, mockProfile, callback);
+
+      expect(updateUser).not.toHaveBeenCalled();
+      expect(handleExistingUser).toHaveBeenCalled();
+      expect(callback).toHaveBeenCalledWith(null, existingUser);
+    });
+
     it('migrates the missing provider id when finding by email fallback (admin path)', async () => {
       const { updateUser } = require('~/models');
       const provider = 'google';
@@ -427,6 +458,36 @@ describe('socialLogin', () => {
       );
     });
 
+    it('does not forward the refresh token as authInfo for non-google providers', async () => {
+      const provider = 'github';
+      const githubId = 'gh-user-123';
+      const email = 'user@example.com';
+
+      const existingUser = {
+        _id: 'ghUser',
+        email,
+        provider: 'github',
+        githubId,
+      };
+
+      findUser.mockResolvedValue(existingUser);
+
+      const mockProfile = {
+        id: githubId,
+        emails: [{ value: email, verified: true }],
+        photos: [{ value: 'https://example.com/avatar.png' }],
+        name: { givenName: 'GitHub', familyName: 'User' },
+      };
+
+      const loginFn = socialLogin(provider, mockGetProfileDetails);
+      const callback = jest.fn();
+
+      await loginFn(null, 'github-refresh-token', null, mockProfile, callback);
+
+      expect(callback).toHaveBeenCalledWith(null, existingUser);
+      expect(callback).not.toHaveBeenCalledWith(null, existingUser, expect.anything());
+    });
+
     it('passes the IdP refresh token through as authInfo when present', async () => {
       const provider = 'google';
       const googleId = 'google-with-refresh';
diff --git a/packages/api/src/auth/exchange.ts b/packages/api/src/auth/exchange.ts
index 53db548f68..8953f9bb54 100644
--- a/packages/api/src/auth/exchange.ts
+++ b/packages/api/src/auth/exchange.ts
@@ -50,6 +50,12 @@ export interface AdminExchangeData {
  */
 export interface AdminExchangeResponse {
   token: string;
+  /**
+   * When Google rotates the refresh token on use, this will differ from the
+   * token the client originally sent. Clients MUST persist this value; failing
+   * to do so causes future refresh calls to fail once Google's original grant
+   * expires or is revoked.
+   */
   refreshToken?: string;
   user: AdminExchangeUser;
   expiresAt?: number;
diff --git a/packages/api/src/auth/googleRefresh.spec.ts b/packages/api/src/auth/googleRefresh.spec.ts
index 2e457ceedd..d767a93026 100644
--- a/packages/api/src/auth/googleRefresh.spec.ts
+++ b/packages/api/src/auth/googleRefresh.spec.ts
@@ -10,6 +10,7 @@ jest.mock('@librechat/data-schemas', () => ({
   ...jest.requireActual('@librechat/data-schemas'),
   logger: {
     debug: jest.fn(),
+    error: jest.fn(),
     info: jest.fn(),
     warn: jest.fn(),
   },
@@ -150,6 +151,21 @@ describe('applyGoogleAdminRefresh', () => {
     });
   });
 
+  it('throws ISSUER_MISMATCH when the id_token aud does not match the configured clientId', async () => {
+    fetchMock.mockResolvedValueOnce(
+      makeOkJson({
+        access_token: 'new-access',
+        id_token: makeIdToken({ sub: SUB, aud: 'wrong-client' }),
+      }),
+    );
+
+    await expect(applyGoogleAdminRefresh(deps, baseOptions)).rejects.toMatchObject({
+      code: 'ISSUER_MISMATCH',
+      status: 401,
+    });
+    expect(deps.findUsers).not.toHaveBeenCalled();
+  });
+
   it('falls back to the userinfo endpoint when id_token is absent', async () => {
     const user = makeUser();
     fetchMock
@@ -222,6 +238,18 @@ describe('applyGoogleAdminRefresh', () => {
     ).rejects.toMatchObject({ code: 'TENANT_MISMATCH', status: 401 });
   });
 
+  it('throws USER_ID_MISMATCH when multiple users share the same googleId', async () => {
+    fetchMock.mockResolvedValueOnce(
+      makeOkJson({ access_token: 'new-access', id_token: makeIdToken() }),
+    );
+    deps.findUsers.mockResolvedValue([makeUser(), makeUser({ email: 'other@example.com' })]);
+
+    await expect(applyGoogleAdminRefresh(deps, baseOptions)).rejects.toMatchObject({
+      code: 'USER_ID_MISMATCH',
+      status: 401,
+    });
+  });
+
   it('throws USER_NOT_FOUND when no admin user matches the refreshed googleId', async () => {
     fetchMock.mockResolvedValueOnce(
       makeOkJson({ access_token: 'new-access', id_token: makeIdToken() }),
diff --git a/packages/api/src/auth/googleRefresh.ts b/packages/api/src/auth/googleRefresh.ts
index 8dee79b732..4c5b63c7fd 100644
--- a/packages/api/src/auth/googleRefresh.ts
+++ b/packages/api/src/auth/googleRefresh.ts
@@ -20,6 +20,7 @@ interface GoogleTokenset {
 
 interface IdTokenClaims {
   sub?: string;
+  aud?: string | string[];
 }
 
 export interface MintedGoogleAdminToken {
@@ -70,7 +71,7 @@ async function resolveSubFromUserinfo(accessToken: string): Promise<string | und
       headers: { Authorization: `Bearer ${accessToken}` },
     });
     if (!response.ok) {
-      logger.warn('[adminGoogleRefresh] userinfo fallback returned non-OK', {
+      logger.warn('[admin/oauth/refresh] userinfo fallback returned non-OK', {
         status: response.status,
       });
       return undefined;
@@ -79,7 +80,7 @@ async function resolveSubFromUserinfo(accessToken: string): Promise<string | und
     return typeof body?.sub === 'string' ? body.sub : undefined;
   } catch (err) {
     const error = err as { name?: string; message?: string };
-    logger.warn('[adminGoogleRefresh] userinfo fallback failed', {
+    logger.warn('[admin/oauth/refresh] userinfo fallback failed', {
       name: error?.name,
       message: error?.message,
     });
@@ -109,7 +110,7 @@ async function fetchGoogleTokenset(
     });
   } catch (err) {
     const error = err as { name?: string; message?: string };
-    logger.warn('[adminGoogleRefresh] token endpoint request failed', {
+    logger.warn('[admin/oauth/refresh] token endpoint request failed', {
       name: error?.name,
       message: error?.message,
     });
@@ -117,7 +118,7 @@ async function fetchGoogleTokenset(
   }
 
   if (!response.ok) {
-    logger.warn('[adminGoogleRefresh] Google rejected refresh grant', {
+    logger.warn('[admin/oauth/refresh] Google rejected refresh grant', {
       status: response.status,
     });
     throw new AdminRefreshError('REFRESH_FAILED', 401, 'Refresh failed');
@@ -127,7 +128,7 @@ async function fetchGoogleTokenset(
     return (await response.json()) as GoogleTokenset;
   } catch (err) {
     const error = err as { name?: string; message?: string };
-    logger.warn('[adminGoogleRefresh] Google returned non-JSON body', {
+    logger.warn('[admin/oauth/refresh] Google returned non-JSON body', {
       name: error?.name,
       message: error?.message,
     });
@@ -135,7 +136,7 @@ async function fetchGoogleTokenset(
   }
 }
 
-async function resolveGoogleSub(tokenset: GoogleTokenset): Promise<string> {
+async function resolveGoogleSub(tokenset: GoogleTokenset, clientId?: string): Promise<string> {
   if (typeof tokenset.access_token !== 'string') {
     throw new AdminRefreshError(
       'IDP_INCOMPLETE',
@@ -147,6 +148,17 @@ async function resolveGoogleSub(tokenset: GoogleTokenset): Promise<string> {
   let sub: string | undefined;
   if (typeof tokenset.id_token === 'string') {
     const claims = decodeJwtPayload(tokenset.id_token);
+    if (clientId && claims?.aud !== undefined) {
+      const aud = claims.aud;
+      const audOk = Array.isArray(aud) ? aud.includes(clientId) : aud === clientId;
+      if (!audOk) {
+        throw new AdminRefreshError(
+          'ISSUER_MISMATCH',
+          401,
+          'id_token aud does not match configured client',
+        );
+      }
+    }
     if (typeof claims?.sub === 'string') {
       sub = claims.sub;
     }
@@ -193,10 +205,18 @@ async function resolveAdminUser(
   const filter = (
     options.tenantId ? { googleId, tenantId: options.tenantId } : { googleId }
   ) as FilterQuery<IUser>;
-  const [found] = await deps.findUsers(filter, SAFE_USER_PROJECTION, {
+  const matches = await deps.findUsers(filter, SAFE_USER_PROJECTION, {
     sort: { updatedAt: -1 },
-    limit: 1,
+    limit: 2,
   });
+  if (matches.length > 1) {
+    logger.error('[admin/oauth/refresh] ambiguous googleId match', {
+      googleId,
+      tenantId: options.tenantId,
+    });
+    throw new AdminRefreshError('USER_ID_MISMATCH', 401, 'Ambiguous identity');
+  }
+  const [found] = matches;
   if (!found) {
     throw new AdminRefreshError('USER_NOT_FOUND', 401, 'No user found for the refreshed identity');
   }
@@ -233,7 +253,7 @@ export async function applyGoogleAdminRefresh(
   };
 
   const tokenset = await fetchGoogleTokenset(configured);
-  const googleId = await resolveGoogleSub(tokenset);
+  const googleId = await resolveGoogleSub(tokenset, configured.clientId);
   const user = await resolveAdminUser(googleId, deps, options);
 
   if (deps.isEmailAllowed && !(await deps.isEmailAllowed(user))) {
@@ -250,6 +270,12 @@ export async function applyGoogleAdminRefresh(
 
   const minted = await deps.mintToken(user);
 
+  if (tokenset.refresh_token && tokenset.refresh_token !== options.refreshToken) {
+    logger.info(
+      '[admin/oauth/refresh] Google rotated the refresh token; client must persist the new value',
+    );
+  }
+
   return {
     token: minted.token,
     refreshToken: tokenset.refresh_token ?? options.refreshToken,