jase64 is a simple tool to encode and decode base64 in json values.
asdf plugin add jase64 https://github.com/ogontaro/asdf-jase64.git
cat data.json
#{
# "key": "value",
# "key2": "dmFsdWU="
#}
jase64 --encode data.json
#{
# "foo": "Zm9vZm9v",
# "bar": "YmFyYmFy"
#}
jase64 --encode data.json > data_encoded.json
jase64 --decode data_encoded.json
#{
# "hoge": "fuga",
# "joy": "full"
#}