How to Fix Auth0 Custom Domain Issues

In this tutorial, you'll learn about How to Fix Auth0 Custom Domain Issues. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

Your Auth0 custom domain shows "SSL certificate error" or does not load. DNS records are misconfigured or the certificate is not issued.

The Wrong Way

# Pointing an A record to Auth0's IP
auth.example.com → 192.0.2.1 (wrong)

Auth0 uses CNAME records, not A records. Auth0's IP addresses can change without notice.

The Right Way

Step 1: Configure DNS CNAME

# For custom domain "auth.example.com":
# DNS CNAME record:
# auth.example.com → YOUR_TENANT.auth0.com
# 
# Wait for DNS propagation:
dig CNAME auth.example.com
# Should show: auth.example.com. 300 IN CNAME your-tenant.auth0.com.

Step 2: Add the custom domain in Auth0

# Auth0 Dashboard → Branding → Custom Domains → "Add Custom Domain"
# Domain: auth.example.com
# Type: "Custom Domain"

Step 3: Verify domain ownership

# Auth0 provides a verification TXT record:
# auth-com.example.com → TXT → "auth0=domain_verification=xxxxx"
# Add this to your DNS
# Click "Verify" in Auth0 dashboard

Step 4: Provision the SSL certificate

# Auth0 automatically provisions a TLS certificate
# from Let's Encrypt
# This can take 5-30 minutes
# Check: "Certificate Status" → "Active"

Custom domain auth.example.com active — SSL certificate valid, login pages served from custom domain, no mixed content warnings.

Prevention

• Set up the custom domain early in the project — DNS propagation takes time.
• Use a dedicated subdomain like auth.example.com or login.example.com.
• The custom domain configuration follows the same pattern as Doda Browser's branded login pages — CNAME + Let's Encrypt for TLS.

Common Mistakes with custom domain

1. Using return to exit a function early instead of wrapping a pure value in the monad
2. Mixing let bindings with <- bindings in do notation, producing type errors
3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world AUTH0 code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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