免费证书
shell:https://github.com/acmesh-official/acme.sh
python:https://github.com/diafygi/acme-tiny
certbot:https://certbot.eff.org/
计费系统
ToughRADIUS 认证计费系统:https://github.com/talkincode/toughradius
CentOS6源
http://file.kangle.odata.cc/repo/Centos-6.repo
http://file.kangle.odata.cc/repo/epel-6.repo