Revert "docs(portal): strip unreleased domain config keys from B16"

This reverts commit cb06161.

Author: sharadregoti

portal/install/custom-domain.mdx

@@ -2,7 +2,7 @@
 title: "Custom Domain Configuration"
 description: "Configure a custom domain for the Tyk Developer Portal, with DNS records, TLS certificates, and nginx reverse proxy setup for a branded HTTPS URL."
 sidebarTitle: "Custom Domain"
-keywords: "Developer Portal, custom domain, HTTPS, TLS, DNS, CNAME, A record, nginx, reverse proxy"
+keywords: "Developer Portal, custom domain, HTTPS, TLS, DNS, CNAME, A record, nginx, reverse proxy, PORTAL_DOMAIN_DEFAULT, PORTAL_DOMAIN_ENABLE_CUSTOM"
 ---
 
 | Edition    | Deployment Type        |
@@ -15,8 +15,9 @@ keywords: "Developer Portal, custom domain, HTTPS, TLS, DNS, CNAME, A record, ng
 
 By default, the Developer Portal is accessible on the hostname or IP address of the server it runs on. A custom domain lets you expose the Live Portal on a URL you control, such as `developers.mycompany.com`, so API consumers see a branded, professional address.
 
-Configuring a custom domain involves two steps:
+Configuring a custom domain involves three steps:
 
+- Setting the domain in the Portal configuration
 - Creating a DNS record that points your domain to the Portal
 - Configuring TLS so the Portal is accessible over HTTPS
 
@@ -27,6 +28,24 @@ Configuring a custom domain involves two steps:
 - Access to your DNS provider to create records
 - A valid TLS certificate and private key for your domain
 
+## Configure the Portal Domain
+
+Two configuration keys control custom domain behavior:
+
+| Config Key | Description |
+| :--------- | :---------- |
+| [`Domain.EnableCustomDomains`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration#portal-domain-enable-custom) | Enables custom domain support. Set to `true`. Env var: `PORTAL_DOMAIN_ENABLE_CUSTOM`. |
+| [`Domain.DefaultDomain`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration#portal-domain-default) | The domain consumers use to access the Live Portal, for example `developers.mycompany.com`. Env var: `PORTAL_DOMAIN_DEFAULT`. |
+
+Add these to your Portal configuration. For how to pass environment variables in your deployment type, see the install guide for [Docker](/portal/install/docker), [Kubernetes](/portal/install/kubernetes), or [Linux](/portal/install/linux).
+
+```ini
+PORTAL_DOMAIN_ENABLE_CUSTOM=true
+PORTAL_DOMAIN_DEFAULT=developers.mycompany.com
+```
+
+Restart the Portal after making this change.
+
 ## Configure DNS
 
 Create a DNS record at your DNS provider that points your custom domain to the Portal:
@@ -132,9 +151,10 @@ After restarting the Portal with the updated configuration:
 
 To change the custom domain after the initial setup:
 
-1. **Create a DNS record** pointing the new domain to the Portal (A record or CNAME, as described above).
-2. **Update your TLS certificate** to cover the new domain, either in `PORTAL_TLS_CERTIFICATES` or on your reverse proxy.
-3. **Restart the Portal** to apply the changes.
+1. **Update `PORTAL_DOMAIN_DEFAULT`** to the new domain value.
+2. **Create a DNS record** pointing the new domain to the Portal (A record or CNAME, as described above).
+3. **Update your TLS certificate** to cover the new domain, either in `PORTAL_TLS_CERTIFICATES` or on your reverse proxy.
+4. **Restart the Portal** to apply the changes.
 
 ## Troubleshooting
 
@@ -143,7 +163,7 @@ To change the custom domain after the initial setup:
     Check that the `Name` field in `PORTAL_TLS_CERTIFICATES` matches the domain exactly, including the subdomain. If you are using a reverse proxy, confirm the proxy certificate covers your custom domain and has not expired.
   </Accordion>
   <Accordion title="The Portal still serves on the old hostname">
-    Confirm that your DNS record is pointing to the correct IP address or hostname and that DNS propagation has completed. If you are using a reverse proxy, verify that `X-Forwarded-Host` is set to your custom domain on every request.
+    Confirm that `PORTAL_DOMAIN_ENABLE_CUSTOM` is set to `true` and that `PORTAL_DOMAIN_DEFAULT` is set to your custom domain. Restart the Portal after making any changes to environment variables.
   </Accordion>
   <Accordion title="SSO callbacks or email links use the wrong host or scheme">
     The Portal constructs base URLs from the `X-Forwarded-Host` and `X-Forwarded-Proto` headers. If these headers are missing or set incorrectly, callbacks and links will use the wrong host or scheme. Check that your reverse proxy sets both headers on every request. See [Single Sign On](/tyk-stack/tyk-developer-portal/enterprise-developer-portal/managing-access/enable-sso) for SSO configuration details.

product-stack/tyk-enterprise-developer-portal/deploy/configuration.mdx

@@ -285,6 +285,16 @@ You can specify any string value in this setting. Omit this setting if you don't
 **Type:** `string` <br/>
 **Description**: Redirects the portal login page to a custom SSO login URL. When set, GET requests to `/auth/password/login` are automatically redirected to this URL, and the portal's "Log in" button points to it. This is useful when using an Identity Provider (IDP) based login/SSO profile, as it allows you to bypass the default portal password login page and direct users to your external IDP login page instead. This setting only affects the login page redirect; user registration and password reset pages remain unchanged.
 
+### PORTAL_DOMAIN_ENABLE_CUSTOM
+**Config file:** Domain.EnableCustomDomains <br/>
+**Type:** `boolean` <br/>
+**Description**: Enables custom domain support for the Developer Portal. When set to `true`, the portal uses the domain specified in `PORTAL_DOMAIN_DEFAULT` as the public-facing URL for the Live Portal instead of inferring it from incoming request headers. The default value is `false`.
+
+### PORTAL_DOMAIN_DEFAULT
+**Config file:** Domain.DefaultDomain <br/>
+**Type:** `string` <br/>
+**Description**: The custom domain that API consumers use to access the Live Portal, for example `developers.mycompany.com`. This setting takes effect only when `PORTAL_DOMAIN_ENABLE_CUSTOM` is set to `true`.
+
 ## Response Headers Configuration
 This section explains how to configure custom HTTP response headers that will be added to all responses from the Portal.