Caddy setup with Cloudflare

Cloud Aug 31, 2021

What we want to achieve

In this post, we'll setup a Caddy reverse proxy situated behind the protections of Cloudflare. We'll setup authenticated TLS pulls, so only connections from Cloudflare servers are allowed and use a Cloudflare certificate to encrypt the data from Caddy to Cloudflare.

  1. Head to SSL/TLS > Origin Server
  1. Click Create Certificate
  2. Select RSA (2048) and you'll probably want a period of over 3 years for convenience.
  1. Create a cert folder.
cd
mkdir cert
cd cert
  1. Using the PEM key format copy and paste the Origin Certificate to example.com.pem and the Private Key into example.com.key.
  1. Add the following line to your Caddyfile
    tls <Path to PEM> <Path to KEY>

Example:

cyberhost.uk {
  tls /file_path/cyberhost.uk.pem /file_path/cyberhost.uk.key
  reverse_proxy 127.0.0.1
}

Reload config: caddy reload

Setup Cloudflare TLS Authenticated Pull

The issue

Cloudflare is used for their industry-leading DDoS and security benefits, so we don't want anyone being able to bypass this protection!

Cloudflare can be bypassed by sending a host header to the origin IP.

Example:
curl --resolve '<DOMAIN>:<PORT>:<Origin-IP>' https://<DOMAIN> -k
curl --resolve 'example.com:443:93.184.216.34' https://example.com -k

The fix

One solution is to use an allowlist/whitelist with Cloudflare's IP Ranges however these can change over time. The best solution is to cryptographically authenticate all clients trying to load your website.

  1. Enable 'Authenticated Origin Pulls' in Cloudflare.
    SSL/TLS -> Origin Server
  1. Get a copy of the Cloudflare Certificate here.

Also available here:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Paste the certificate into a file e.g /file_path/origin-pull-ca.pem

  1. Now extend the tls directive in your Caddyfile to add client auth
cyberhost.uk {
  tls /file_path/cyberhost.uk.pem /file_path/cyberhost.uk.key {
    client_auth {
      mode require_and_verify
      trusted_ca_cert_file /file_path/origin-pull-ca.pem
      }
   }
   reverse_proxy 127.0.0.1
}
  1. Now when we try to bypass Cloudflare we are denied access!

curl --resolve 'example.com:443:93.184.216.34' https://example.com -k

Error:
curl: (56) OpenSSL SSL_read: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate, errno 0

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Tags

CyberHost

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