WeChat applet development uses letsencrypt.sh script to configure free https certificate for nginx under Centos 6.8.

# wget https://raw.githubusercontent.com/xdtianyu/scripts/master/lets-encrypt/letsencrypt.conf
# wget https://raw.githubusercontent.com/xdtianyu/scripts/master/lets-encrypt/letsencrypt.sh

# vim letsencrypt.conf
 
# only modify the values, key files will be generated automaticly.
ACCOUNT_KEY="letsencrypt-account.key" 
DOMAIN_KEY="mtian.net.key"
DOMAIN_DIR="/usr/local/nginx/html"  #网站的根目录
DOMAINS="DNS:mtian.net,DNS:www.mtian.net" #你的网站域名，多个域名用,号分隔
#ECC=TRUE
#LIGHTTPD=TRUE

添加执行权限并执行
# chmod +x letsencrypt.sh   
# ./letsencrypt.sh letsencrypt.conf  
 
运行完成后会在当前目录生成如下文件
letsencrypt-account.key  lets-encrypt-x3-cross-signed.pem  mtian.csr
letsencrypt.conf         mtian.chained.crt                 mtian.net.key
letsencrypt.sh           mtian.crt

# vim /usr/local/nginx/conf/nginx.conf
 
 
    
    server {
        listen       443 ssl;
        server_name  www.mtian.net;
 
        ssl on;
         
        ssl_certificate /usr/local/nginx/conf/mtian.chained.crt;
        ssl_certificate_key /usr/local/nginx/conf/mtian.net.key;
 
 
        location / {
            root   html;
            index  index.html index.htm;
        }
    }

# cp  mtian.chained.crt /usr/local/nginx/conf/
# cp  mtian.net.key  /usr/local/nginx/conf/

# service nginx restart
 
Stopping nginx:                                            [  OK  ]
Starting nginx:                                            [  OK  ]