How to Fix Caddy TLS Certificate Error

In this tutorial, you'll learn about How to Fix Caddy TLS Certificate Error. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

Caddy fails to provision a TLS certificate with [ERROR] obtaining certificate: acme: error: 403 or uses a self-signed certificate instead of Let's Encrypt — the ACME challenge cannot complete or DNS validation fails.

The Problem

2026/06/24 10:00:00 [ERROR] obtaining certificate: acme: error: 403
urn:ietf:params:acme:error:unauthorized :::
The client lacks sufficient authorization

Step-by-Step Fix

Step 1: Check DNS resolves to the Caddy server

dig +short example.com
# Must return the public IP of your Caddy server

Step 2: Ensure port 80 is accessible

# Caddy uses HTTP-01 challenge by default
nc -zv example.com 80

Step 3: Use DNS challenge for wildcards

example.com {
    tls {
        dns cloudflare YOUR_API_TOKEN
    }
    reverse_proxy localhost:3000
}

Step 4: Use custom certificate

example.com {
    tls /etc/ssl/certs/example.crt /etc/ssl/private/example.key
    reverse_proxy localhost:3000
}

Step 5: Set ACME server to staging for testing

{
    acme_ca https://acme-staging-v02.api.letsencrypt.org/directory
}

Step 6: Check certificate renewal

caddy renew --force

Prevention Tips

• Use DNS challenge for production to avoid port 80 dependency
• Set up monitoring for certificate expiry
• Keep ACME account private key secure
• Use the staging ACME endpoint for initial testing

Common Mistakes with tls cert

1. Using foldl instead of foldl' causing stack overflow on large lists
2. Forgetting deriving (Show, Eq) on custom data types needed for debugging
3. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable

These mistakes appear frequently in real-world CADDY 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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