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:

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:

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.

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
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
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
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
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

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 to example.com for cross-surface reuse
TLS Policy	tls_policy on the domain controls minimum TLS version / cipher posture for Auth0-managed certs. Default recommended. Set at create or via PATCH
Custom Client IP Header	custom_client_ip_header tells Auth0 which request header carries the real client IP when traffic passes through a reverse proxy. Valid values: true-client-ip, cf-connecting-ip, x-forwarded-for, x-azure-clientip. Set at create or via PATCH
Domain Metadata	Up to 10 custom key-value pairs attached to a custom domain (keys and values ≤ 255 chars). Read from Actions via event.custom_domain.domain_metadata for per-domain logic (region, brand, env tagging)

Full schema and token / iss behavior live in references/advanced.md.

Prerequisites

These apply to any capability that writes to the tenant. Check domain health is read-only and can be run first to verify these.

Auth0 Management API access

All capabilities use the Management API. Either:

• The Auth0 CLI (auth0 ...) authenticated to the target tenant (auth0 tenants use <name>), or
• A Machine-to-Machine application with the scopes in references/api.md.

Check the active tenant immediately before the first Auth0 CLI command in a capability, not at skill invocation. Do not check the tenant before the user has chosen a capability. If a capability uses only non-CLI tools (e.g., DNS lookups, Cloudflare MCP, direct Management API calls via curl), skip the tenant check entirely.

When the chosen capability does use the Auth0 CLI, run this before the first CLI command:

auth0 tenants list

Look for the row marked as active (or check the active field in the JSON output). Show the active tenant to the user and ask them to confirm it is the intended target. If it's wrong, stop and have the user run:

auth0 tenants use <tenant-name>

Then re-confirm before proceeding. For mutating calls (create, PATCH, delete), require explicit confirmation. For read-only CLI flows, surfacing the tenant name (and naming it in the output report) is enough — still never assume the active tenant is correct based on conversational context alone.

DNS provider access (for Set up, Troubleshoot, and Remove)

Set up a custom domain writes a CNAME. Remove a custom domain deletes one. Troubleshoot verification may suggest a fix that requires a DNS edit. What the skill needs depends on the provider tier:

• Tier 1 Cloudflare: Cloudflare MCP connected. If not, skill prompts the user to run claude mcp add --transport http cloudflare https://mcp.cloudflare.com/mcp and authorize in the browser.
• Tier 2 AWS Route 53: AWS credentials configured (env vars, shared config, or SSO session). Verified with aws sts get-caller-identity.
• Tier 3 Azure DNS: Azure CLI signed in. Verified with az account show.
• Tier 4 other: no programmatic access; user manually adds the record in their provider's dashboard.

Plan requirements for automation: None of the three automated tiers require a paid plan on the DNS provider side. Cloudflare DNS record CRUD via the MCP works on the Free plan (Free zones created after Sept 2024 cap at 200 DNS records per zone; Auth0's CNAME counts as one). Route 53 is pay-per-use (~$0.50/hosted zone/month + query costs, not in AWS free tier). Azure DNS is subscription-based with no tier gating; the signed-in identity needs the DNS Zone Contributor role. Full detail per tier in the per-provider sub-files under references/providers/ (router: references/providers.md).

Credit card on file (Free-tier tenants)

Custom domains are available on all plan tiers including Free. Free tenants need a credit card on file for identity verification (card is not charged). Without one, POST /custom-domains returns 403. Fix at Dashboard → Tenant Settings → Billing (or the Teams section for Teams-managed tenants).

Surface this as the likely cause on any 403 rather than suggesting a plan upgrade.

Common Mistakes

Quick index; each entry links to the canonical treatment in the relevant capability file.

Mistake	See
Assuming a 403 on create means plan upgrade	api.md error codes
Removing the CNAME after verification (breaks cert renewal)	capability-5 interpreting results
Using a subdomain with passkeys without setting relying_party_identifier	capability-3 RPID section
Trying to change certificate type via PATCH	capability-3 scope note
Enabling DNS proxy on the CNAME (Cloudflare orange cloud)	capability-2 proxy check
Enabling CNAME flattening on the zone	capability-2 flattening check
Deleting and recreating to "unstick" verification	capability-2 what not to do
Not updating SDK domain / issuerBaseURL after verification	capability-1 report next steps
Calling Management API via tenant domain under MCD	advanced.md auth0-custom-domain header

Related Skills

• auth0-branding: Customize Universal Login appearance (page templates require a verified custom domain)
• auth0-organizations: Organization-specific branding for B2B multi-tenancy

References

• references/capability-setup.md: Set up a custom domain
• references/capability-troubleshoot.md: Troubleshoot verification
• references/capability-manage.md: Manage existing domains
• references/capability-remove.md: Remove a custom domain
• references/capability-health.md: Check domain health
• references/providers.md: DNS provider router — NS → provider map; links into per-provider sub-files under references/providers/ (cloudflare.md, route53.md, azure-dns.md, manual.md). Open only the sub-file matching the detected provider.
• references/examples.md: cURL samples plus end-to-end CI/CD automation and multi-environment patterns
• references/api.md: Endpoint reference, CLI commands, error codes, scopes
• references/advanced.md: MCD, default-domain, auth0-custom-domain header, self-managed certs, token iss behavior, verification troubleshooting deep-dive

External Docs

• Custom Domains Overview
• Auth0-Managed Certificates
• Self-Managed Certificates
• Multiple Custom Domains
• Default Custom Domain
• Configure Features to Use Custom Domains
• Troubleshoot Custom Domains
• Cloudflare MCP Server