diff --git a/packages/core/src/app/init.ts b/packages/core/src/app/init.ts
index 4ffdb811c..5ac044aff 100644
--- a/packages/core/src/app/init.ts
+++ b/packages/core/src/app/init.ts
@@ -29,7 +29,7 @@ export default async function initApp(app: Koa): Promise<void> {
       return next();
     }
 
-    const tenantId = await getTenantId(ctx.URL);
+    const [tenantId, isCustomDomain] = await getTenantId(ctx.URL);
 
     if (!tenantId) {
       ctx.status = 404;
@@ -37,7 +37,11 @@ export default async function initApp(app: Koa): Promise<void> {
       return next();
     }
 
-    const tenant = await trySafe(tenantPool.get(tenantId), (error) => {
+    // If the request is a custom domain of the tenant, use the custom endpoint to build "OIDC issuer"
+    // otherwise, build from the default endpoint (subdomain).
+    const customEndpoint = isCustomDomain ? ctx.URL.origin : undefined;
+
+    const tenant = await trySafe(tenantPool.get(tenantId, customEndpoint), (error) => {
       ctx.status = error instanceof TenantNotFoundError ? 404 : 500;
       void appInsights.trackException(error);
     });
diff --git a/packages/core/src/env-set/index.ts b/packages/core/src/env-set/index.ts
index 7fb599dac..88c14e63d 100644
--- a/packages/core/src/env-set/index.ts
+++ b/packages/core/src/env-set/index.ts
@@ -63,7 +63,7 @@ export class EnvSet {
     return this.#oidc;
   }
 
-  async load() {
+  async load(customDomain?: string) {
     const pool = await createPoolByEnv(
       this.databaseUrl,
       EnvSet.values.isUnitTest,
@@ -77,7 +77,9 @@ export class EnvSet {
     });
 
     const oidcConfigs = await getOidcConfigs();
-    const endpoint = getTenantEndpoint(this.tenantId, EnvSet.values);
+    const endpoint = customDomain
+      ? new URL(customDomain)
+      : getTenantEndpoint(this.tenantId, EnvSet.values);
     this.#oidc = await loadOidcValues(appendPath(endpoint, '/oidc').href, oidcConfigs);
   }
 
diff --git a/packages/core/src/middleware/koa-spa-session-guard.ts b/packages/core/src/middleware/koa-spa-session-guard.ts
index f5c8f01dd..66ebf5623 100644
--- a/packages/core/src/middleware/koa-spa-session-guard.ts
+++ b/packages/core/src/middleware/koa-spa-session-guard.ts
@@ -52,7 +52,7 @@ export default function koaSpaSessionGuard<
           return;
         }
 
-        const tenantId = await getTenantId(ctx.URL);
+        const [tenantId] = await getTenantId(ctx.URL);
 
         if (!tenantId) {
           throw new RequestError({ code: 'session.not_found', status: 404 });
diff --git a/packages/core/src/routes/interaction/actions/submit-interaction.mfa.test.ts b/packages/core/src/routes/interaction/actions/submit-interaction.mfa.test.ts
index 0549bb916..9d3fbe9ae 100644
--- a/packages/core/src/routes/interaction/actions/submit-interaction.mfa.test.ts
+++ b/packages/core/src/routes/interaction/actions/submit-interaction.mfa.test.ts
@@ -36,7 +36,7 @@ mockEsm('@logto/shared', () => ({
 }));
 
 mockEsm('#src/utils/tenant.js', () => ({
-  getTenantId: () => adminTenantId,
+  getTenantId: () => [adminTenantId],
 }));
 
 const userQueries = {
diff --git a/packages/core/src/routes/interaction/actions/submit-interaction.test.ts b/packages/core/src/routes/interaction/actions/submit-interaction.test.ts
index 0dea2ab9a..bc9007ac8 100644
--- a/packages/core/src/routes/interaction/actions/submit-interaction.test.ts
+++ b/packages/core/src/routes/interaction/actions/submit-interaction.test.ts
@@ -37,7 +37,7 @@ mockEsm('@logto/shared', () => ({
 }));
 
 mockEsm('#src/utils/tenant.js', () => ({
-  getTenantId: () => adminTenantId,
+  getTenantId: () => [adminTenantId],
 }));
 
 const userQueries = {
diff --git a/packages/core/src/routes/interaction/actions/submit-interaction.ts b/packages/core/src/routes/interaction/actions/submit-interaction.ts
index 861922e42..5ca004ab3 100644
--- a/packages/core/src/routes/interaction/actions/submit-interaction.ts
+++ b/packages/core/src/routes/interaction/actions/submit-interaction.ts
@@ -105,7 +105,8 @@ async function handleSubmitRegister(
   const { client_id } = ctx.interactionDetails.params;
 
   const { isCloud } = EnvSet.values;
-  const isInAdminTenant = (await getTenantId(ctx.URL)) === adminTenantId;
+  const [currentTenantId] = await getTenantId(ctx.URL);
+  const isInAdminTenant = currentTenantId === adminTenantId;
   const isCreatingFirstAdminUser =
     isInAdminTenant && String(client_id) === adminConsoleApplicationId && !(await hasActiveUsers());
 
diff --git a/packages/core/src/routes/user-assets.ts b/packages/core/src/routes/user-assets.ts
index d69841729..fa52bde44 100644
--- a/packages/core/src/routes/user-assets.ts
+++ b/packages/core/src/routes/user-assets.ts
@@ -63,7 +63,7 @@ export default function userAssetsRoutes<T extends AuthedRouter>(...[router]: Ro
         'guard.mime_type_not_allowed'
       );
 
-      const tenantId = await getTenantId(ctx.URL);
+      const [tenantId] = await getTenantId(ctx.URL);
       assertThat(tenantId, 'guard.can_not_get_tenant_id');
 
       const { storageProviderConfig } = SystemContext.shared;
diff --git a/packages/core/src/tenants/Tenant.ts b/packages/core/src/tenants/Tenant.ts
index 4963febf4..3d24be56d 100644
--- a/packages/core/src/tenants/Tenant.ts
+++ b/packages/core/src/tenants/Tenant.ts
@@ -36,10 +36,11 @@ import type TenantContext from './TenantContext.js';
 import { getTenantDatabaseDsn } from './utils.js';
 
 export default class Tenant implements TenantContext {
-  static async create(id: string, redisCache: RedisCache): Promise<Tenant> {
+  static async create(id: string, redisCache: RedisCache, customDomain?: string): Promise<Tenant> {
     // Treat the default database URL as the management URL
     const envSet = new EnvSet(id, await getTenantDatabaseDsn(id));
-    await envSet.load();
+    // Custom endpoint is used for building OIDC issuer URL when the request is a custom domain
+    await envSet.load(customDomain);
 
     return new Tenant(envSet, id, new WellKnownCache(id, redisCache));
   }
diff --git a/packages/core/src/tenants/index.ts b/packages/core/src/tenants/index.ts
index 31d7586e1..5225a2d6c 100644
--- a/packages/core/src/tenants/index.ts
+++ b/packages/core/src/tenants/index.ts
@@ -15,8 +15,9 @@ export class TenantPool {
     },
   });
 
-  async get(tenantId: string): Promise<Tenant> {
-    const tenantPromise = this.cache.get(tenantId);
+  async get(tenantId: string, customDomain?: string): Promise<Tenant> {
+    const cacheKey = `${tenantId}-${customDomain ?? 'default'}`;
+    const tenantPromise = this.cache.get(cacheKey);
 
     if (tenantPromise) {
       const tenant = await tenantPromise;
@@ -27,9 +28,9 @@ export class TenantPool {
       // Otherwise, create a new tenant instance and store in LRU cache, using the code below.
     }
 
-    consoleLog.info('Init tenant:', tenantId);
-    const newTenantPromise = Tenant.create(tenantId, redisCache);
-    this.cache.set(tenantId, newTenantPromise);
+    consoleLog.info('Init tenant:', tenantId, customDomain);
+    const newTenantPromise = Tenant.create(tenantId, redisCache, customDomain);
+    this.cache.set(cacheKey, newTenantPromise);
 
     return newTenantPromise;
   }
diff --git a/packages/core/src/utils/tenant.test.ts b/packages/core/src/utils/tenant.test.ts
index fac175546..f91b2771b 100644
--- a/packages/core/src/utils/tenant.test.ts
+++ b/packages/core/src/utils/tenant.test.ts
@@ -23,6 +23,11 @@ mockEsm('#src/queries/domains.js', () => ({
 
 const { getTenantId } = await import('./tenant.js');
 
+const getTenantIdFirstElement = async (url: URL) => {
+  const [tenantId] = await getTenantId(url);
+  return tenantId;
+};
+
 describe('getTenantId()', () => {
   const backupEnv = process.env;
 
@@ -37,7 +42,7 @@ describe('getTenantId()', () => {
       DEVELOPMENT_TENANT_ID: 'foo',
     };
 
-    await expect(getTenantId(new URL('https://some.random.url'))).resolves.toBe('foo');
+    await expect(getTenantIdFirstElement(new URL('https://some.random.url'))).resolves.toBe('foo');
 
     process.env = {
       ...backupEnv,
@@ -46,20 +51,22 @@ describe('getTenantId()', () => {
       DEVELOPMENT_TENANT_ID: 'bar',
     };
 
-    await expect(getTenantId(new URL('https://some.random.url'))).resolves.toBe('bar');
+    await expect(getTenantIdFirstElement(new URL('https://some.random.url'))).resolves.toBe('bar');
   });
 
   it('should resolve proper tenant ID for similar localhost endpoints', async () => {
-    await expect(getTenantId(new URL('http://localhost:3002/some/path////'))).resolves.toBe(
-      adminTenantId
-    );
-    await expect(getTenantId(new URL('http://localhost:30021/some/path'))).resolves.toBe(
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:3002/some/path////'))
+    ).resolves.toBe(adminTenantId);
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:30021/some/path'))
+    ).resolves.toBe(defaultTenantId);
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhostt:30021/some/path'))
+    ).resolves.toBe(defaultTenantId);
+    await expect(getTenantIdFirstElement(new URL('https://localhost:3002'))).resolves.toBe(
       defaultTenantId
     );
-    await expect(getTenantId(new URL('http://localhostt:30021/some/path'))).resolves.toBe(
-      defaultTenantId
-    );
-    await expect(getTenantId(new URL('https://localhost:3002'))).resolves.toBe(defaultTenantId);
   });
 
   it('should resolve proper tenant ID for similar domain endpoints', async () => {
@@ -69,24 +76,30 @@ describe('getTenantId()', () => {
       ENDPOINT: 'https://foo.*.logto.mock/app',
     };
 
-    await expect(getTenantId(new URL('https://foo.foo.logto.mock/app///asdasd'))).resolves.toBe(
-      'foo'
-    );
-    await expect(getTenantId(new URL('https://foo.*.logto.mock/app'))).resolves.toBe(undefined);
-    await expect(getTenantId(new URL('https://foo.foo.logto.mockk/app///asdasd'))).resolves.toBe(
+    await expect(
+      getTenantIdFirstElement(new URL('https://foo.foo.logto.mock/app///asdasd'))
+    ).resolves.toBe('foo');
+    await expect(getTenantIdFirstElement(new URL('https://foo.*.logto.mock/app'))).resolves.toBe(
       undefined
     );
-    await expect(getTenantId(new URL('https://foo.foo.logto.mock/appp'))).resolves.toBe(undefined);
-    await expect(getTenantId(new URL('https://foo.foo.logto.mock:1/app/'))).resolves.toBe(
+    await expect(
+      getTenantIdFirstElement(new URL('https://foo.foo.logto.mockk/app///asdasd'))
+    ).resolves.toBe(undefined);
+    await expect(getTenantIdFirstElement(new URL('https://foo.foo.logto.mock/appp'))).resolves.toBe(
       undefined
     );
-    await expect(getTenantId(new URL('http://foo.foo.logto.mock/app'))).resolves.toBe(undefined);
-    await expect(getTenantId(new URL('https://user.foo.bar.logto.mock/app'))).resolves.toBe(
-      undefined
-    );
-    await expect(getTenantId(new URL('https://foo.bar.bar.logto.mock/app'))).resolves.toBe(
+    await expect(
+      getTenantIdFirstElement(new URL('https://foo.foo.logto.mock:1/app/'))
+    ).resolves.toBe(undefined);
+    await expect(getTenantIdFirstElement(new URL('http://foo.foo.logto.mock/app'))).resolves.toBe(
       undefined
     );
+    await expect(
+      getTenantIdFirstElement(new URL('https://user.foo.bar.logto.mock/app'))
+    ).resolves.toBe(undefined);
+    await expect(
+      getTenantIdFirstElement(new URL('https://foo.bar.bar.logto.mock/app'))
+    ).resolves.toBe(undefined);
   });
 
   it('should resolve proper tenant ID if admin localhost is disabled', async () => {
@@ -99,17 +112,21 @@ describe('getTenantId()', () => {
       ADMIN_DISABLE_LOCALHOST: '1',
     };
 
-    await expect(getTenantId(new URL('http://localhost:5000/app///asdasd'))).resolves.toBe(
-      undefined
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:5000/app///asdasd'))
+    ).resolves.toBe(undefined);
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:3002/app///asdasd'))
+    ).resolves.toBe(undefined);
+    await expect(getTenantIdFirstElement(new URL('https://user.foo.logto.mock/app'))).resolves.toBe(
+      'foo'
     );
-    await expect(getTenantId(new URL('http://localhost:3002/app///asdasd'))).resolves.toBe(
-      undefined
+    await expect(
+      getTenantIdFirstElement(new URL('https://user.admin.logto.mock/app//'))
+    ).resolves.toBe(undefined); // Admin endpoint is explicitly set
+    await expect(getTenantIdFirstElement(new URL('https://admin.logto.mock/app'))).resolves.toBe(
+      adminTenantId
     );
-    await expect(getTenantId(new URL('https://user.foo.logto.mock/app'))).resolves.toBe('foo');
-    await expect(getTenantId(new URL('https://user.admin.logto.mock/app//'))).resolves.toBe(
-      undefined
-    ); // Admin endpoint is explicitly set
-    await expect(getTenantId(new URL('https://admin.logto.mock/app'))).resolves.toBe(adminTenantId);
 
     process.env = {
       ...backupEnv,
@@ -118,9 +135,9 @@ describe('getTenantId()', () => {
       ENDPOINT: 'https://user.*.logto.mock/app',
       ADMIN_DISABLE_LOCALHOST: '1',
     };
-    await expect(getTenantId(new URL('https://user.admin.logto.mock/app//'))).resolves.toBe(
-      'admin'
-    );
+    await expect(
+      getTenantIdFirstElement(new URL('https://user.admin.logto.mock/app//'))
+    ).resolves.toBe('admin');
   });
 
   it('should resolve proper tenant ID for path-based multi-tenancy', async () => {
@@ -132,16 +149,24 @@ describe('getTenantId()', () => {
       PATH_BASED_MULTI_TENANCY: '1',
     };
 
-    await expect(getTenantId(new URL('http://localhost:5000/app///asdasd'))).resolves.toBe('app');
-    await expect(getTenantId(new URL('http://localhost:3002///bar///asdasd'))).resolves.toBe(
-      adminTenantId
-    );
-    await expect(getTenantId(new URL('https://user.foo.logto.mock/app'))).resolves.toBe(undefined);
-    await expect(getTenantId(new URL('https://user.admin.logto.mock/app//'))).resolves.toBe(
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:5000/app///asdasd'))
+    ).resolves.toBe('app');
+    await expect(
+      getTenantIdFirstElement(new URL('http://localhost:3002///bar///asdasd'))
+    ).resolves.toBe(adminTenantId);
+    await expect(getTenantIdFirstElement(new URL('https://user.foo.logto.mock/app'))).resolves.toBe(
       undefined
     );
-    await expect(getTenantId(new URL('https://user.logto.mock/app'))).resolves.toBe(undefined);
-    await expect(getTenantId(new URL('https://user.logto.mock/app/admin'))).resolves.toBe('admin');
+    await expect(
+      getTenantIdFirstElement(new URL('https://user.admin.logto.mock/app//'))
+    ).resolves.toBe(undefined);
+    await expect(getTenantIdFirstElement(new URL('https://user.logto.mock/app'))).resolves.toBe(
+      undefined
+    );
+    await expect(
+      getTenantIdFirstElement(new URL('https://user.logto.mock/app/admin'))
+    ).resolves.toBe('admin');
   });
 
   it('should resolve proper custom domain', async () => {
@@ -151,6 +176,6 @@ describe('getTenantId()', () => {
       NODE_ENV: 'production',
     };
     findActiveDomain.mockResolvedValueOnce({ domain: 'logto.mock.com', tenantId: 'mock' });
-    await expect(getTenantId(new URL('https://logto.mock.com'))).resolves.toBe('mock');
+    await expect(getTenantIdFirstElement(new URL('https://logto.mock.com'))).resolves.toBe('mock');
   });
 });
diff --git a/packages/core/src/utils/tenant.ts b/packages/core/src/utils/tenant.ts
index d33c66e42..7223265de 100644
--- a/packages/core/src/utils/tenant.ts
+++ b/packages/core/src/utils/tenant.ts
@@ -53,6 +53,9 @@ export const clearCustomDomainCache = async (url: URL | string) => {
   await trySafe(async () => redisCache.delete(getDomainCacheKey(url)));
 };
 
+/**
+ * Get tenant ID from the custom domain URL.
+ */
 const getTenantIdFromCustomDomain = async (
   url: URL,
   pool: CommonQueryMethods
@@ -74,7 +77,15 @@ const getTenantIdFromCustomDomain = async (
   return domain?.tenantId;
 };
 
-export const getTenantId = async (url: URL) => {
+/**
+ * Get tenant ID from the current request's URL.
+ *
+ * @param url The current request's URL
+ * @returns The tenant ID and whether the URL is a custom domain
+ */
+export const getTenantId = async (
+  url: URL
+): Promise<[tenantId: string | undefined, isCustomDomain: boolean]> => {
   const {
     values: {
       isMultiTenancy,
@@ -90,28 +101,28 @@ export const getTenantId = async (url: URL) => {
   const pool = await sharedPool;
 
   if (adminUrlSet.deduplicated().some((endpoint) => isEndpointOf(url, endpoint))) {
-    return adminTenantId;
+    return [adminTenantId, false];
   }
 
   if ((!isProduction || isIntegrationTest) && developmentTenantId) {
     consoleLog.warn(`Found dev tenant ID ${developmentTenantId}.`);
 
-    return developmentTenantId;
+    return [developmentTenantId, false];
   }
 
   if (!isMultiTenancy) {
-    return defaultTenantId;
+    return [defaultTenantId, false];
   }
 
   if (isPathBasedMultiTenancy) {
-    return matchPathBasedTenantId(urlSet, url);
+    return [matchPathBasedTenantId(urlSet, url), false];
   }
 
   const customDomainTenantId = await getTenantIdFromCustomDomain(url, pool);
 
   if (customDomainTenantId) {
-    return customDomainTenantId;
+    return [customDomainTenantId, true];
   }
 
-  return matchDomainBasedTenantId(urlSet.endpoint, url);
+  return [matchDomainBasedTenantId(urlSet.endpoint, url), false];
 };