A simple tool for decoding & encoding data saved in acme.sh conf files, denoted by __ACME_BASE64__START_ & __ACME_BASE64__END_.

acmebase64

#!/bin/sh

ts=__ACME_BASE64__START_
te=__ACME_BASE64__END_
case $# in
	0)
		# loop ensures no final newline is added to input
		printf '%s%s%s\n' "$ts" "$(
			q=false
			f='%s'
			until $q; do
				IFS= read -r l || q=true
				printf "$f" "$l"
				f='\n%s'
			done | base64 -w0
		)" "$te"
		;;
	1)
		if ! [ "$1" = -d ]; then
			echo 'only understand the option "-d" for decode' >&2
			exit 1
		fi
		grep -Po "$ts\K.*?(?=$te)" | head -n1 | base64 -d
		;;
	*)
		echo 'too many options' >&2
		exit 1
		;;
esac

It reads from stdin, and writes to stdout. See what the current value is with the decode option, e.g. this reads the first one found in a conf file:

./acmebase64 -d < .acme.sh/domain.example_ecc/domain.example.conf

This encodes a command, omitting the trailing newline like acme does:

printf '%s' '/path/to/my/script -x -y '\''z z z'\'' foo.bar' | ./acmebase64

Confirm the correct input was encoded by piping the result to ./acmebase64 -d, again., and inspecting its output.