Create API Key on Github

• My Profile
• API Tokens
• Create Token
• Edit zone DNS (Template)
• Change permissions from Edit to Read (I tested this with Edit)
• Add your domains/zones under Zone Resource
• Add your IPv(4/6) under Client IP Adress Filtering
• Click on Continue to summary
• Click on Create Token
• Copy your Key

Set SSL/TLS encryption mode to Full (strict)

Add your (Sub-)Domain record with enabled Proxy status

Add the following part into your Caddyfile for your (Sub-)Domain:

    tls {
        dns cloudflare <api_key>
    }

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// Credits: https://samjmck.com/en/blog/using-caddy-with-cloudflare/

or (for linux) set env value like this:

echo "export CLOUDFLARE_AUTH_TOKEN=TOKEN_HERE" >> ~/.bashrc
source ~/.bashrc

and you can use this in caddy:

    tls {
        dns cloudflare {env.CLOUDFLARE_AUTH_TOKEN}
    }

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If you get this error on startup: module not registered: dns.providers.cloudflare

Download (and replace your currently binary file) a custom version on https://caddyserver.com/download with caddy-dns/cloudflare as feature.