Sets the acme_ca option in the global options block of the resulting Caddyfile. The URL to the ACME CA’s directory. It is strongly recommended to set this to https://acme-staging-v02.api.letsencrypt.org/directory for Let’s Encrypt’s staging endpoint while testing or in development. Value null should be prefered for production setups, as it omits the acme_ca option to enable automatic issuer fallback.

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"https://acme-v02.api.letsencrypt.org/directory"