auth0-custom-domains

What this skill does

# Auth0 Custom Domains

Drive Auth0 custom-domain work end-to-end: Auth0 Management API, DNS provider, verification polling, and the configuration that stitches everything together. Detects the user's DNS provider (Cloudflare, Route 53, Azure DNS, or other) and automates record creation when the provider supports it.

## Overview

This skill is **capability-based**, not step-based. It groups the work a user might want to do into five distinct capabilities (setup, troubleshoot, manage, remove, health check), each with its own flow in a dedicated reference file. The main SKILL.md acts as a lobby: it holds the capabilities table, key concepts, prerequisites, and common mistakes that apply across all flows. When a user invokes the skill, pick the matching capability from the table, load its reference file, and follow that flow.

The capability design matches how users actually come to Auth0 custom domain work: "set one up," "mine is broken," "change something," "remove one," or "is my setup still working?" Each intent maps to a distinct flow with its own safety checks and hand-offs.

## Interaction style

Ask questions as plain conversational text. Never use structured UI widgets (e.g., AskUserQuestion) except for a single yes/no confirmation immediately before a destructive or irreversible action (create, PATCH, delete). For everything else:

- **Capability routing**: present a numbered list and wait for the user to reply
- **Input gathering**: ask one focused question at a time; wait for a response before asking the next
- **Free-form values** (hostnames, domain names, etc.): just ask directly — don't wrap them in a widget that forces a click before typing

Example of the right pattern for capability routing:

```text
What do you want to do?

1. Set up a custom domain
2. Troubleshoot verification
3. Manage an existing domain
4. Remove a domain
5. Check domain health (read-only, safe starting point)
```

Example of the right pattern for a single input:

```text
What's the hostname you want to set up? (e.g., login.example.com)
```

## Error-code triage — CHECK THIS FIRST

If the user's message is primarily about an HTTP error code from the Management API (e.g., "I got a 403", "why is this returning 409?", a pasted error body, a log entry with a status code), **answer from this table first.** Do not default to general Auth0 knowledge — it leads to wrong advice on the Free-tier 403 case in particular. Only after the error-code answer, offer to route into the matching capability if the user wants to continue (e.g., "want me to walk through Set up with that fix in place?").

| Status and context | Correct diagnosis and fix |
|---|---|
| **403** on `POST /custom-domains` (Free tier) | **Not a plan-tier problem.** Custom domains are available on **all plans including Free** (confirmed in Auth0 docs: *"To set up a free custom domain, Auth0 tenants must have a valid credit card on file for verification purposes and fraud prevention. The credit card will not be charged."*). Fix at **Dashboard → Tenant Settings → Billing** by adding a card. **Do NOT suggest a plan upgrade.** |
| **403** on `POST /custom-domains` with `type: self_managed_certs` | This *is* a plan issue. Self-managed certs are Enterprise-only. Either downgrade to `type: auth0_managed_certs` (works on all plans) or upgrade to Enterprise. |
| **409** on `POST /custom-domains` | Domain already exists on this tenant or another. Run `auth0 domains list` to check; if on another tenant the user owns, delete it there first. Do not retry a fresh create. |
| **400** on `PATCH /custom-domains/{id}` with `type` in body | `type` is fixed at create time and rejected by PATCH. Route to delete (capability 4) + recreate (capability 1). Warn about auth downtime during the cutover. |
| **400** with `operation_not_supported` on `relying_party_identifier` | Feature-flag gate on the tenant. Retry without `relying_party_identifier` and ask Auth0 support to enable the flag. |
| **404** on any custom-domain endpoint | Wrong `custom_domain_id`, or wrong tenant. Verify with `auth0 tenants list` + `auth0 domains list`. |
| **429** | Rate limited. Back off; the skill's verify-poll backoff pattern (5s, 10s, 20s, 30s, 60s) avoids this. |

Full error-code reference with all cases and resolutions: [references/api.md#error-codes](references/api.md#error-codes).

## Capabilities

When this skill is invoked and the user is NOT asking about an error code, ask the user which capability they want using a plain numbered list (see Interaction style above). Route to **Check domain health** first when the user reports a problem without a specific known cause, or when they're unsure which capability they need; it's the safe, read-only starter that will point them to the right follow-up.

| # | Capability | What it does |
|---|---|---|
| 1 | **Set up a custom domain** | End-to-end: create the domain in Auth0, detect the DNS provider, write the CNAME record (automated on Cloudflare / Route 53 / Azure; guided on other providers), verify ownership, and report what to update in the user's apps. Handles first-time setup and adding to MCD. See [references/capability-setup.md](references/capability-setup.md) |
| 2 | **Troubleshoot verification** | Domain stuck in `pending_verification` or verification failing. Diagnostic ladder: compare DNS to expected, check for proxies / CNAME flattening / conflicting records / propagation / private-zone issues, then retry. See [references/capability-troubleshoot.md](references/capability-troubleshoot.md) |
| 3 | **Manage existing domains** | Surgical edits on already-configured domains: set or change the default (for MCD), update TLS policy, configure the custom client IP header, set the relying party identifier for passkeys, manage per-domain metadata (up to 10 key-value pairs readable from Actions), list domains and show status. Intent-driven. Certificate type is fixed at create time; PATCH rejects `type` changes. See [references/capability-manage.md](references/capability-manage.md) |
| 4 | **Remove a custom domain** | Delete a domain safely: warn if it's the default, surface dependent applications, delete in Auth0, clean up the CNAME in DNS. See [references/capability-remove.md](references/capability-remove.md) |
| 5 | **Check domain health** | Read-only: list all custom domains, check DNS records match expected values, surface default-domain config, flag anything needing attention. Safe starter capability. See [references/capability-health.md](references/capability-health.md) |

Pick a capability, then follow the flow in its reference file. The **Prerequisites** and **Key Concepts** sections below apply across all capabilities.

## Key Concepts

| Concept | Description |
|---|---|
| CNAME Record | DNS record pointing your custom domain to Auth0's edge (e.g., `{tenant}.edge.tenants.auth0.com`). Must stay in DNS permanently for certificate renewal |
| Auth0-Managed Certificate | Auth0 provisions and auto-renews TLS certs every ~3 months. Default and recommended. Type is fixed at create time and cannot be changed via PATCH |
| Self-Managed Certificate | TLS terminates at a reverse proxy (Cloudflare, CloudFront, Azure Front Door, or GCP LB). Enterprise only; verification uses TXT instead of CNAME. Type is fixed at create time and cannot be changed via PATCH; to change, delete and recreate the domain |
| NS Detection | Looking up the root domain's nameservers to identify the DNS provider and route to the correct automation tier |
| Multiple Custom Domains (MCD) | Enterprise feature; up to 20 domains per tenant for multi-brand or multi-region |
| Default Custom Domain | When MCD is configured, the domain used when a Management API call doesn't send the `auth0-custom-domain` header |
| Relying Party Identifier (RPID) | Per-domain `relying_party_identifier` that decouples the custom domain hostname from the passkey `rpId`. Set at create or via PATCH. Lets you serve auth at `login.example.com` while passkeys bind t