SDK Configuration for Multiple Custom Domains

When using multiple custom domains, you need to configure your Auth0 SDKs to use the appropriate custom domain for authentication. This guide covers SDK configuration for different platforms and scenarios.

Key concepts

Domain parameter

All Auth0 SDKs require a domain parameter that specifies which Auth0 domain to use for authentication. When using custom domains, set this parameter to your custom domain instead of your Auth0 canonical domain. Without custom domain:

domain: 'tenant.auth0.com'

With custom domain:

domain: 'login.example.com'

Token issuer

When using a custom domain, tokens will have the iss (issuer) claim set to your custom domain:

{
  "iss": "https://login.example.com/",
  "sub": "auth0|123456",
  "aud": "your-client-id"
}

You must configure your token validation to accept your custom domain as a valid issuer.

Authentication SDKs

When using MCD, the Customer is responsible for providing and validating all custom domains. When configuring SDKs to resolve tenant custom domains via the domain resolver functions, you are responsible for ensuring that all resolved domains are trusted. Misconfiguring the domain resolver can lead to authentication bypass on the relying party or expose the application to server-side request forgery. Failure to properly configure your domains and proxy servers can create critical security vulnerabilities for which Okta is not liable.

Auth0 SPA SDK (JavaScript)

For single-page applications using the Auth0 SPA SDK:

Next.js

For Next.js applications using the Auth0 Next.js SDK (v4+): Key concepts for MCD with Next.js:

Single Auth0 tenant, multiple domains: All custom domains share the same clientId and clientSecret since they belong to the same Auth0 tenant.
DomainResolver function: The domain parameter accepts a function (config: { headers: Headers; url?: URL }) => Promise<string> | string. This allows dynamic domain resolution per request based on the incoming request headers.
Instance caching: The SDK automatically caches Auth0Client instances per domain using a bounded LRU cache (max 100 entries) for performance.
Session isolation: Sessions created via one custom domain are isolated to that domain and cannot be used interchangeably with sessions from another domain.
URL parameter: The url parameter in the resolver is undefined in Server Components and Server Actions; it is only available in middleware or API routes.

Discovery cache tuning: Configure OIDC metadata caching with the discoveryCache option:

const auth0 = new Auth0Client({
  // ... other config
  discoveryCache: {
    ttl: 600,      // Cache for 10 minutes (default)
    maxEntries: 100  // Max cached issuers (default: 100, LRU eviction)
  }
});

Auth0 React SDK

For React applications using the Auth0 React SDK:

import { Auth0Provider } from '@auth0/auth0-react';

function App() {
  return (
    <Auth0Provider
      domain="login.example.com"
      clientId="YOUR_CLIENT_ID"
      authorizationParams={{
        redirect_uri: window.location.origin
      }}
    >
      <MyApp />
    </Auth0Provider>
  );
}

For multi-domain scenarios:

import { Auth0Provider } from '@auth0/auth0-react';

function App() {
  // Determine custom domain based on environment or context
  const auth0Domain = process.env.REACT_APP_AUTH0_DOMAIN || 'login.example.com';

  return (
    <Auth0Provider
      domain={auth0Domain}
      clientId={process.env.REACT_APP_AUTH0_CLIENT_ID}
      authorizationParams={{
        redirect_uri: window.location.origin
      }}
    >
      <MyApp />
    </Auth0Provider>
  );
}

Auth0.js

For applications using Auth0.js:

const webAuth = new auth0.WebAuth({
  domain: 'login.example.com',
  clientID: 'YOUR_CLIENT_ID',
  redirectUri: window.location.origin + '/callback',
  responseType: 'code',
  scope: 'openid profile email'
});

// Initiate login
webAuth.authorize();

Node.js (Express)

For Node.js applications using express-openid-connect:

const { auth } = require('express-openid-connect');

app.use(
  auth({
    authRequired: false,
    auth0Logout: true,
    issuerBaseURL: 'https://login.example.com',  // Your custom domain
    baseURL: 'http://localhost:3000',
    clientID: 'YOUR_CLIENT_ID',
    secret: 'YOUR_CLIENT_SECRET'
  })
);

For multi-tenant scenarios:

const { auth } = require('express-openid-connect');

// Middleware to determine custom domain per request
app.use((req, res, next) => {
  // Extract tenant identifier from subdomain, path, or header
  const tenant = req.subdomains[0] || 'default';

  // Map tenant to custom domain
  const domainMap = {
    'customer1': 'login.customer1.com',
    'customer2': 'login.customer2.com',
    'default': 'login.example.com'
  };

  req.auth0Domain = domainMap[tenant] || domainMap.default;
  next();
});

// Dynamic auth configuration
app.use((req, res, next) => {
  auth({
    authRequired: false,
    auth0Logout: true,
    issuerBaseURL: `https://${req.auth0Domain}`,
    baseURL: req.protocol + '://' + req.get('host'),
    clientID: process.env.AUTH0_CLIENT_ID,
    secret: process.env.AUTH0_CLIENT_SECRET
  })(req, res, next);
});

Mobile SDKs

iOS (Swift)

Using Auth0.swift:

import Auth0

let auth0 = Auth0
    .webAuth(clientId: "YOUR_CLIENT_ID", domain: "login.example.com")

auth0
    .scope("openid profile email")
    .start { result in
        switch result {
        case .success(let credentials):
            print("Obtained credentials: \(credentials)")
        case .failure(let error):
            print("Failed with: \(error)")
        }
    }

For dynamic domain selection:

import Auth0

class AuthService {
    private let clientId = "YOUR_CLIENT_ID"

    func getAuth0Domain() -> String {
        // Determine domain based on app configuration
        if let savedDomain = UserDefaults.standard.string(forKey: "auth0Domain") {
            return savedDomain
        }
        return "login.example.com" // Default
    }

    func login(completion: @escaping (Result<Credentials, Error>) -> Void) {
        Auth0
            .webAuth(clientId: clientId, domain: getAuth0Domain())
            .scope("openid profile email")
            .start { result in
                completion(result)
            }
    }
}

Android (Kotlin)

Using Auth0.Android:

import com.auth0.android.Auth0
import com.auth0.android.authentication.AuthenticationAPIClient
import com.auth0.android.provider.WebAuthProvider
import com.auth0.android.result.Credentials

val account = Auth0.getInstance(
    "YOUR_CLIENT_ID",
    "login.example.com"  // Your custom domain
)

WebAuthProvider.login(account)
    .withScheme("demo")
    .withScope("openid profile email")
    .start(this, object : Callback<Credentials, AuthenticationException> {
        override fun onSuccess(credentials: Credentials) {
            // Handle success
        }

        override fun onFailure(exception: AuthenticationException) {
            // Handle failure
        }
    })

For multi-domain support:

class AuthManager(private val context: Context) {
    private val clientId = "YOUR_CLIENT_ID"

    private fun getAuth0Domain(): String {
        // Retrieve from shared preferences or app config
        val prefs = context.getSharedPreferences("auth", Context.MODE_PRIVATE)
        return prefs.getString("auth0_domain", "login.example.com") ?: "login.example.com"
    }

    fun login(callback: Callback<Credentials, AuthenticationException>) {
        val account = Auth0.getInstance(clientId, getAuth0Domain())

        WebAuthProvider.login(account)
            .withScheme("demo")
            .withScope("openid profile email")
            .start(context, callback)
    }
}

React Native

Using react-native-auth0:

import Auth0 from 'react-native-auth0';

const auth0 = new Auth0({
  domain: 'login.example.com',
  clientId: 'YOUR_CLIENT_ID'
});

// Login
auth0.webAuth
  .authorize({
    scope: 'openid profile email'
  })
  .then(credentials => {
    console.log('Logged in!');
  })
  .catch(error => {
    console.log(error);
  });

Flutter

Using flutter_auth0:

import 'package:auth0_flutter/auth0_flutter.dart';

final auth0 = Auth0(
  'login.example.com',
  'YOUR_CLIENT_ID'
);

// Login
try {
  final credentials = await auth0.webAuthentication().login();
  print('Logged in successfully');
} catch (e) {
  print('Login failed: $e');
}

Management SDKs

Management SDKs are used to interact with the Auth0 Management API. When using custom domains, you may need to include the auth0-custom-domain header or use the default domain.

Node.js Management SDK

import { ManagementClient, CustomDomainHeader } from "auth0";

// Global custom domain (sent on all whitelisted requests)
const management = new ManagementClient({
  domain: 'tenant.auth0.com',
  clientId: 'YOUR_M2M_CLIENT_ID',
  clientSecret: 'YOUR_M2M_CLIENT_SECRET',
  withCustomDomainHeader: 'login.example.com', 
});

// List users (whitelisted endpoint - header is sent automatically)
const users = await management.users.getAll();

// Per-request override (takes precedence over global)
const reqOptions = {
  ...CustomDomainHeader("specific-user-request.exampleco.com"),
};
const response = await management.users.getAll({}, reqOptions);

Python Management SDK

from auth0.management import ManagementClient, CustomDomainHeader

# Global custom domain (sent on all whitelisted requests)
client = ManagementClient(
    domain='tenant.auth0.com',
    client_id='YOUR_M2M_CLIENT_ID',
    client_secret='YOUR_M2M_CLIENT_SECRET',
    custom_domain='login.example.com',
)

# List users (whitelisted endpoint - header is sent automatically)
users = client.users.list()

# Per-request override (takes precedence over global)
client.users.create(
    connection='Username-Password-Authentication',
    email='user@example.com',
    password='SecurePass123!',
    request_options=CustomDomainHeader('login.brand2.com'),
)

Go Management SDK

import (
    "context"
    management "github.com/auth0/go-auth0/v2/management/client"
    "github.com/auth0/go-auth0/v2/management/option"
)

// Client-level: auto-applies custom domain header to whitelisted endpoints
mgmt, err := management.New(
    "{yourDomain}",
    option.WithClientCredentials("{yourClientId}", "{yourClientSecret}"),
    option.WithCustomDomainHeader("login.example.com"),
)
if err != nil {
    // Handle error
}

// List users (whitelisted endpoint - header is sent automatically)
userList, err := mgmt.Users.List(context.Background(), nil)

// Per-request override (takes precedence over client-level)
userList, err := mgmt.Users.List(
    context.Background(),
    nil,
    option.WithCustomDomainHeader("specific-request.exampleco.com"),
)

Token validation

When using custom domains, update your token validation to accept the custom domain as the issuer.

Node.js (Express)

Using express-jwt or jose:

const { expressjwt } = require('express-jwt');
const { expressJwtSecret } = require('jwks-rsa');

app.use(
  expressjwt({
    secret: expressJwtSecret({
      cache: true,
      rateLimit: true,
      jwksUri: 'https://login.example.com/.well-known/jwks.json'  // Custom domain
    }),
    audience: 'YOUR_API_IDENTIFIER',
    issuer: 'https://login.example.com/',  // Custom domain as issuer
    algorithms: ['RS256']
  })
);

For multiple custom domains:

const validIssuers = [
  'https://login.brand1.com/',
  'https://login.brand2.com/',
  'https://login.example.com/'
];

app.use(
  expressjwt({
    secret: expressJwtSecret({
      cache: true,
      rateLimit: true,
      jwksRequestsPerMinute: 5,
      jwksUri: (req) => {
        // Extract issuer from token to determine JWKS URI
        const token = req.headers.authorization?.split(' ')[1];
        if (token) {
          const payload = JSON.parse(Buffer.from(token.split('.')[1], 'base64').toString());
          return `${payload.iss}.well-known/jwks.json`;
        }
        return 'https://login.example.com/.well-known/jwks.json';
      }
    }),
    audience: 'YOUR_API_IDENTIFIER',
    issuer: validIssuers,  // Accept multiple issuers
    algorithms: ['RS256']
  })
);

Python (Flask)

Using python-jose:

from jose import jwt
from functools import wraps
from flask import request, jsonify

def get_token_auth_header():
    auth = request.headers.get('Authorization', None)
    if not auth:
        raise Exception('Authorization header is expected')

    parts = auth.split()
    if parts[0].lower() != 'bearer':
        raise Exception('Authorization header must start with Bearer')
    elif len(parts) == 1:
        raise Exception('Token not found')
    elif len(parts) > 2:
        raise Exception('Authorization header must be Bearer token')

    return parts[1]

def requires_auth(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        token = get_token_auth_header()

        # Support multiple custom domains
        valid_issuers = [
            'https://login.brand1.com/',
            'https://login.brand2.com/',
            'https://login.example.com/'
        ]

        try:
            # Get JWKS from custom domain
            unverified = jwt.get_unverified_header(token)
            issuer = jwt.get_unverified_claims(token)['iss']

            if issuer not in valid_issuers:
                raise Exception('Invalid issuer')

            jwks_uri = f"{issuer}.well-known/jwks.json"
            jwks = requests.get(jwks_uri).json()

            payload = jwt.decode(
                token,
                jwks,
                algorithms=['RS256'],
                audience='YOUR_API_IDENTIFIER',
                issuer=valid_issuers
            )
        except Exception as e:
            return jsonify({'error': str(e)}), 401

        return f(*args, **kwargs)

    return decorated

Java (Spring Boot)

Using Spring Security:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Value("${auth0.audience}")
    private String audience;

    @Value("${auth0.custom-domain}")
    private String customDomain;

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
            .mvcMatchers("/api/public").permitAll()
            .mvcMatchers("/api/private").authenticated()
            .and()
            .oauth2ResourceServer()
            .jwt()
            .decoder(jwtDecoder());
    }

    @Bean
    JwtDecoder jwtDecoder() {
        String issuerUri = "https://" + customDomain + "/";

        NimbusJwtDecoder jwtDecoder = JwtDecoders.fromIssuerLocation(issuerUri);

        // Validate audience
        OAuth2TokenValidator<Jwt> audienceValidator = new AudienceValidator(audience);
        OAuth2TokenValidator<Jwt> withIssuer = JwtValidators.createDefaultWithIssuer(issuerUri);
        OAuth2TokenValidator<Jwt> withAudience = new DelegatingOAuth2TokenValidator<>(withIssuer, audienceValidator);

        jwtDecoder.setJwtValidator(withAudience);

        return jwtDecoder;
    }
}

Environment-specific configuration

Use environment variables to manage custom domains across environments:

.env file structure

# Development
AUTH0_DOMAIN=dev.example.com
AUTH0_CLIENT_ID=dev_client_id
AUTH0_CLIENT_SECRET=dev_client_secret

# Staging
# AUTH0_DOMAIN=staging.example.com
# AUTH0_CLIENT_ID=staging_client_id
# AUTH0_CLIENT_SECRET=staging_client_secret

# Production
# AUTH0_DOMAIN=login.example.com
# AUTH0_CLIENT_ID=prod_client_id
# AUTH0_CLIENT_SECRET=prod_client_secret

Loading configuration

require('dotenv').config();

const auth0Config = {
  domain: process.env.AUTH0_DOMAIN,
  clientId: process.env.AUTH0_CLIENT_ID,
  clientSecret: process.env.AUTH0_CLIENT_SECRET
};

Troubleshooting

Common issues

Issue	Cause	Solution
Invalid issuer error	Token validation expects canonical domain but receives custom domain	Update token validation to accept custom domain as issuer
JWKS fetch fails	JWKS URI points to canonical domain	Update JWKS URI to use custom domain: `https://custom-domain/.well-known/jwks.json`
Redirect URI mismatch	Callback URL doesn’t match configured redirect URIs	Add custom domain callback URL to application settings
Cross-origin errors (CORS)	Custom domain not in allowed origins	Add custom domain to Allowed Web Origins in application settings
Lock fails to load	Missing `configurationBaseUrl`	Add `configurationBaseUrl` parameter with regional CDN URL

Best practices

Use environment variables: Store custom domains in environment-specific configuration files
Validate multiple issuers: If using multiple custom domains, configure token validation to accept all as valid issuers
Update callback URLs: Ensure all custom domains are added to Allowed Callback URLs in application settings
Test thoroughly: Test authentication through each custom domain before going to production
Monitor token issuers: Log and monitor the iss claim in tokens to ensure correct custom domain usage
Document domain mappings: Maintain clear documentation of which applications use which custom domains
Handle failures gracefully: Implement proper error handling for authentication failures
Cache JWKS: Cache JWKS data to improve performance and reduce requests

Brand Customization

Code Customization

Third-Party Customization

SDK Configuration for Multiple Custom Domains

Key concepts

Domain parameter

Token issuer

Authentication SDKs

Auth0 SPA SDK (JavaScript)

Next.js

Auth0 React SDK

Auth0.js

Node.js (Express)

Mobile SDKs

iOS (Swift)

Android (Kotlin)

React Native

Flutter

Management SDKs

Node.js Management SDK

Python Management SDK

Go Management SDK

Token validation

Node.js (Express)

Python (Flask)

Java (Spring Boot)

Environment-specific configuration

.env file structure

Loading configuration

Troubleshooting

Common issues

Best practices

Learn more

Brand Customization

Code Customization

Third-Party Customization

​Key concepts

​Domain parameter

​Token issuer

​Authentication SDKs

​Auth0 SPA SDK (JavaScript)

​Next.js

​Auth0 React SDK

​Auth0.js

​Node.js (Express)

​Mobile SDKs

​iOS (Swift)

​Android (Kotlin)

​React Native

​Flutter

​Management SDKs

​Node.js Management SDK

​Python Management SDK

​Go Management SDK

​Token validation

​Node.js (Express)

​Python (Flask)

​Java (Spring Boot)

​Environment-specific configuration

​.env file structure

​Loading configuration

​Troubleshooting

​Common issues

​Best practices

​Learn more

Key concepts

Domain parameter

Token issuer

Authentication SDKs

Auth0 SPA SDK (JavaScript)

Next.js

Auth0 React SDK

Auth0.js

Node.js (Express)

Mobile SDKs

iOS (Swift)

Android (Kotlin)

React Native

Flutter

Management SDKs

Node.js Management SDK

Python Management SDK

Go Management SDK

Token validation

Node.js (Express)

Python (Flask)

Java (Spring Boot)

Environment-specific configuration

.env file structure

Loading configuration

Troubleshooting

Common issues

Best practices

Learn more