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If you’re using Authsignal’s pre-built UI for your authentication flows you can add your own custom domain.

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Add your custom domain to the Authsignal Portal

Decide on the subdomain you want to use.
For example, if your app is hosted on example.com, you might want to use auth.example.com as your custom domain.
Now, head to the custom domains page in the Authsignal Portal. Enter your desired subdomain and click Add. You will be prompted to add a CNAME record to your DNS provider. Once Authsignal detects that the CNAME record has been added, you will see a Valid configuration message. Click Activate custom domain to get the pre-built UI to use your custom domain.
You must activate your custom domain before it will take effect.
Custom domain activated

An active custom domain in the Authsignal Portal.

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Multiple custom domains

Multiple custom domains is an enterprise feature. Contact us to enable this for your account.
If you have multiple applications or brands, you can configure additional custom domains. Each domain can be used independently with Authsignal’s pre-built UI.

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Use cases

Multiple custom domains offers flexibility for organizations managing diverse branding, regional requirements, or partner integrations—all from a single Authsignal tenant.
  • Multiple brands, single tenant — Organizations owning several brands can maintain separate branded authentication experiences (e.g., auth.brand1.com and auth.brand2.com) while sharing a centralized Authsignal configuration.
  • Regional domains — Businesses requiring different domains for regional operations can serve users across jurisdictions (e.g., auth.example.com, auth.example.co.uk, auth.example.com.au).
  • White-labeled B2B SaaS — SaaS providers offering white-labeled solutions can give each customer their own branded authentication domain (e.g., auth.client-a.com, auth.client-b.com) while maintaining a single tenant.

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Adding additional domains

Once the multiple custom domains feature is enabled for your account, you’ll see an Add another custom domain option on the custom domains page. Follow the same setup process as your first domain:
  1. Enter the subdomain (e.g., mfa.anotherbrand.com)
  2. Add the CNAME record to your DNS provider
  3. Wait for verification
  4. Click Activate custom domain

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Default domain

One of your custom domains is designated as the default. This is the domain used when you don’t explicitly specify which domain to use in your integration. To change the default domain, click Set as default on any active domain.

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Using a specific domain

To redirect a user to a specific domain, you can include a customDomain attribute in your track action request. 
const request = {
  userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
  action: "signIn",
  attributes: {
    redirectUrl: "https://yourapp.com/callback",
    customDomain: "https://auth.example.com"
  },
};

const response = await authsignal.track(request);

const url = response.url;
The customDomain attribute must be the full URL of the domain you want to use, including the protocol (e.g. https://auth.example.com).
If no customDomain is specified or the domain is not active, the default domain will be used.