Caddy Cors Allow Anything Setup

Caddyfile

# Global options
{
    email [email protected]
    debug
}

(cors) {
  @cors_preflight method OPTIONS

  handle @cors_preflight {
    header Access-Control-Allow-Origin "*"
    header Access-Control-Allow-Methods "*"
    header Access-Control-Allow-Headers "*"
    header Access-Control-Allow-Credentials "true"
    header Access-Control-Max-Age "86400"
    respond "" 204
  }

  header Access-Control-Allow-Origin "*"
  header Access-Control-Allow-Credentials "true"
  header Access-Control-Expose-Headers "*"
}

listmonk.skeptrune.com {
        import cors
        reverse_proxy localhost:9000
}

You can use this config on any domain you are hosing via caddy to make sure that all cors requests to it succeed