mTLS 认证

Wed, 12 Apr 2023 21:18:30 +0800

有时候虽然我们部署一个服务到了公网，但只想提供给部分用户而不想其他人（黑客/robot）使用，比如webhook或者跨机房的服务调用。虽然我们可以使用密码/token保护这些服务，但是程序可以被直接扫描到，仍然存在被攻击的风险。而如果把这些服务放在某个认证服务器后面，又存在二次登陆的问题。如何标识目标用户又不影响请求过程？答案是mTLS认证。
TLS认证是当前WEB通信的基石，没有加密的通信无异于裸奔：任何中间人都可以查看/串改通信内容。mTLS认证，亦即双向TLS认证，不但客户端校验服务器证书，服务器亦校验客户端证书，这意味着如果客户端证书不在服务器的信任列表里面，那么客户端也访问不了服务。请求认证过程如下

mTLS可以用来保护私有服务，加强通信过程，减少服务器攻击。由于客户端也需要提供证书，证书里面可以携带用户或者设备信息，可以识别仅授信用户，才授权访问。由于服务器需要校验客户端信息，所以未提供有效证书用户不能访问，就算盗取了用户的密码/token也不可以。因为双方都互相校验证书，所以也可以抵抗中间人攻击。这样子我们便可以公开服务，但又限制某些用户使用了。
mTLS认证有别于应用程序认证。mTLS仅涉及证书校验，在网关出就可以进行，不需要涉及应用程序逻辑/数据库。mTLS也不依赖于请求头/请求体里面的内容，所以不会影响已有程序。
mTLS认证限制某些用户/设备访问，也有别于传统VPN网络。VPN总是要求服务端/客户端先建立连接，才能在同一内网内访问。一旦连接建立，便可以访问所有服务。而采用mTLS认证，则每一个服务都可以使用不同的客户端证书，限制不同的用户访问。零信任（ZeroTrust）亦建立在mTLS之上，即对每个请求都做双向认证。
mTLS并不是什么新鲜事物，许多互联网软件都支持，比如浏览器、SSH，SSH采用私钥登陆的过程，即双向认证：客户端先将自己的公钥上传至服务器，建立连接时，客户端询问是否信任服务器，服务器亦校验客户端。Git使用SSH key登陆也是类似双向认证。开发者调用Google云服务，除了app认证信息，也是需要双向认证的。有些互联网公司也采用双向认证来保护自己的应用，比如支付功能，甚至是所有页面-只允许自己的APP查看，其他免谈。
Nginx早已支持mTLS认证，除了服务器本身的证书，还需要配置客户端证书或其签发root CA证书。关于服务器证书获取之前已介绍基于DNS自动获取证书了，同样的方法也可以用来生成客户端证书，比如基于用户id来生成不同域名username.id.example.com的证书给客户端使用。这里介绍另外一种基于LEGO ACME在本地生成客户端证书的方法。
首先安装lego程序，如果有golang环境直接就好了，或者下载对应平台的程序。

$ go install github.com/go-acme/lego/v4/cmd/lego@latest

然后就可以基于DNS厂商来生成证书，这里以腾讯云DNS，注意它的APP Key是不同于DNSPod的。如果网络不加，建议延长TIMEOUT时间。这里一并生成浏览器/系统可用的PKCS12文件(.pfx)

$ TENCENTCLOUD_SECRET_ID=*** TENCENTCLOUD_PROPAGATION_TIMEOUT=120 TENCENTCLOUD_POLLING_INTERVAL=5 \ 
TENCENTCLOUD_SECRET_KEY=***\
lego --email username@exmaple.com --pem --pfx --pfx.pass *** --cert.timeout 120 --dns tencentcloud --domains user1.idt.exmaple.com run

2023/04/08 11:42:46 [INFO] [user1.idt.exmaple.com] acme: Obtaining bundled SAN certificate
2023/04/08 11:42:47 [INFO] [user1.idt.exmaple.com] AuthURL: https://acme-v02.api.letsencrypt.org/acme/authz-v3/217627103547
2023/04/08 11:42:47 [INFO] [user1.idt.exmaple.com] acme: Could not find solver for: tls-alpn-01
2023/04/08 11:42:47 [INFO] [user1.idt.exmaple.com] acme: Could not find solver for: http-01
2023/04/08 11:42:47 [INFO] [user1.idt.exmaple.com] acme: use dns-01 solver
2023/04/08 11:42:47 [INFO] [user1.idt.exmaple.com] acme: Preparing to solve DNS-01
2023/04/08 11:42:50 [INFO] [user1.idt.exmaple.com] acme: Trying to solve DNS-01
2023/04/08 11:42:50 [INFO] [user1.idt.exmaple.com] acme: Checking DNS record propagation using [127.0.0.53:53]
2023/04/08 11:42:55 [INFO] Wait for propagation [timeout: 2m0s, interval: 5s]
2023/04/08 11:42:55 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:01 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:06 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:11 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:17 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:22 [INFO] [user1.idt.exmaple.com] acme: Waiting for DNS record propagation.
2023/04/08 11:43:35 [INFO] [user1.idt.exmaple.com] The server validated our request
2023/04/08 11:43:35 [INFO] [user1.idt.exmaple.com] acme: Cleaning DNS-01 challenge
2023/04/08 11:43:37 [INFO] [user1.idt.exmaple.com] acme: Validations succeeded; requesting certificates
2023/04/08 11:43:39 [INFO] [user1.idt.exmaple.com] Server responded with a certificate.
$ ls -la .lego/certificates
total 40
drwx------ 2 channing channing 4096 4月 8 11:43 .
drwx------ 4 channing channing 4096 4月 8 10:58 ..
-rw------- 1 channing channing 5341 4月 8 11:43 user1.idt.exmaple.com.crt
-rw------- 1 channing channing 3751 4月 8 11:43 user1.idt.exmaple.com.issuer.crt
-rw------- 1 channing channing 244 4月 8 11:43 user1.idt.exmaple.com.json
-rw------- 1 channing channing 227 4月 8 11:43 user1.idt.exmaple.com.key
-rw------- 1 channing channing 5568 4月 8 11:43 user1.idt.exmaple.com.pem
-rw------- 1 channing channing 2992 4月 8 11:43 user1.idt.exmaple.com.pfx

由于这个证书的CA是Let’s Encrypt的，而Let’s Encrypt本身的证书又是Internet Security Research Group签发。而当Nginx配置ssl_client_certificate CA证书时只能是Root CA，也就是ISRG的证书，而不是中间厂商的证书，也就是不能用Let’s Encrypt的CA证书。ISRG的证书可以从浏览器导出或者网上下载，然后保存到服务器上

$ mv isrg_root.crt /etc/nginx/certs/
$ chomd 400 etc/nginx/certs/isrg_root.crt

Nginx配置如下，可以将日志级别设置为debug,调试/观察认证

$ vim /etc/nginx/conf.d/site-available/100-mtls.example.com
server {
 listen 80;
 server_name mtls.example.com;
 return 301 https://$host$request_uri;
}

server {

 listen 443 ssl;
 server_name mtls.example.com;

 ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
 ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
 ssl_client_certificate /etc/nginx/conf.d/certs/isrg_root.crt;
 ssl_verify_client on;
 ssl_verify_depth 2;

 ssl_session_cache builtin:1000 shared:SSL:10m;
 ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
 ssl_ciphers HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
 ssl_prefer_server_ciphers on;
# error_log /var/log/nginx/error.log debug;
 location / {
 root /var/www/mtls.example.com/html;
 index index.html index.htm;
 }
 error_page 500 502 503 504 /50x.html;
 location = /50x.html {
 root /usr/share/nginx/html;
 }
}

使用curl测试一下，提示需要客户端证书

curl https://mtls.example.com
<html>
 <head>
 <title>400 No required SSL certificate was sent</title>
 </head>

 <body bgcolor="white">
 <center>
 <h1>400 Bad Request</h1>
 </center>
 <center>No required SSL certificate was sent</center>
 <hr>
 <center>nginx/1.14.0</center>
 </body>
</html>

当带上证书的时候就可以了

curl --cert user1.idt.exmaple.com.crt --key user1.idt.exmaple.com.key https://mtls.example.com
<html>
<head>
<title>Welcome to mtls.example.com!</title>
</head>
<body>
<h1>Success! The mtls server is working!</h1>
</body>
</html>

使用浏览器访问目标网站需要安装.pfx文件，否则也会报错，禁止访问。通常Windows/Mac双击.pfx文件即可自动安，也可以通过浏览器配置来安装。使用Chrome需要在从菜单设置->隐私设置和安全性->安全->管理设备证书->个人->导入。使用Firefox则是从从菜单设置->隐私与安全->安全->查看证书->您的证书->导入。iOS和Android可以通过邮件的方式将.pfx文件传输到手机上，点击.pfx文件按照系统提示安装即可。最后使用浏览器打开https://mtls.example.com，会提示使用刚才配置好的证书，选择即可。
上面Nginx配置的是公共CA的根证书（isrg_root.crt），这意味着所有该CA签发的证书都将可以访问https://mtls.example.com，这有点太开放了。如果我们自己生成Root CA证书，便可以做进一步的控制。
首先生成Root CA证书

$ openssl genrsa -des3 -out ca.key 4096
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
$ openssl req -new -x509 -days 3650 -key ca.key -out ca.crt39:06
Enter pass phrase for ca.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:
Email Address []:

$ cat ca.key > ca.pem 
$ cat ca.crt >> ca.pem
$ ls
ca.crt ca.key ca.pem

然后使用CA证书生成客户端

$ openssl genrsa -out user1.key
Enter PEM pass phrase:
$ openssl req -new -key user1.key -out user1.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
$ openssl x509 -req -days 365 -in user1.csr -CA ca.crt -CAkey ca.key -set_serial 01 -out user1.crt
Certificate request self-signature ok
Enter pass phrase for ca.key:
$ openssl pkcs12 -export -out user1.pfx -inkey user1.key -in user1.crt -certfile ca.crt
Enter Export Password:
Verifying - Enter Export Password:

然后将ca.crt上传至服务器/etc/nginx/certs/下面并配置ssl_client_certificate使用该证书即可。使用curl测试一下


curl --cert user1.crt --key user1.key https://mtls.example.com
<html>
<head>
<title>Welcome to mtls.example.com!</title>
</head>
<body>
<h1>Success! The mtls server is working!</h1>
</body>
</html>

同样可以成功访问。不过刚才生成的.pfx文件只有Firefox可以导入使用，其他系统/浏览器不可以，那么可以从Firefox中重新备份导出该文件，Chrome/其他系统就可以使用了。或者重新转换一下

openssl pkcs12 -in user1.pfx -out user1.pem -nodes #pfx证书转换为x.509格式的pem证书
openssl pkcs12 -in user1.pfx -nocerts -nodes -out user1.key #pfx证书中提取密钥对
openssl rsa -in user1.key -out user1_private.key #密钥对提取私钥
openssl pkcs12 -export -in user1.pem -inkey user1_private.key -out user1.pfx #使用x.509+私钥转换为win10可用的pfx证书

使用自定义CA可以有效控制证书的签发，也可以免CA直接签发客户端证书

$ openssl req -x509 -nodes -days 9999 -newkey rsa:2048 -keyout user2.key -out user2.crt
..+...+...
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:
Email Address []

无CA签名的证书，就直接将user2.crt上传至服务器/etc/nginx/certs/下面并配置ssl_client_certificate使用该证书即可。如果生成了多个，就合并成一个上传服务器就好了。使用curl测试一下，也是可以的

curl --cert user2.crt --key user2.key https://mtls.example.com
<html>
<head>
<title>Welcome to mtls.example.com!</title>
</head>
<body>
<h1>Success! The mtls server is working!</h1>
</body>
</html>

Nginx还支持将客户端证书及CA的DN传递给后端程序，再配合访问控制，便可以精细控制用户访问了。Nginx配置如下，注意这里ssl_verify_client是optional,认证失败不再返回400而是403

$ vim /etc/nginx/conf.d/site-available/100-mtls.example.com
server {
 listen 443 ssl;
 server_name mtls.example.com;

 ssl_certificate /etc/letsencrypt/live/example.comfullchain.pem;
 ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
 ssl_client_certificate /etc/nginx/conf.d/certs/ca.crt;
 ssl_verify_client optional;
 ssl_verify_depth 2;

 ssl_session_cache builtin:1000 shared:SSL:10m;
 ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
 ssl_ciphers HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
 ssl_prefer_server_ciphers on;
# error_log /var/log/nginx/error.log debug;
 location / {
# if ($ssl_client_i_dn != "/C=EX/CN=Client/emailAddress=user1@example.com") {
# return 403;
# }
 if ($ssl_client_verify != SUCCESS) { return 403; }
 proxy_set_header SSL_Client_Issuer $ssl_client_i_dn;
 proxy_set_header SSL_Client $ssl_client_s_dn;
 proxy_set_header SSL_Client_Verify $ssl_client_verify;
 proxy_pass http://127.0.0.1:3000/;
 }
 error_page 500 502 503 504 /50x.html;
 location = /50x.html {
 root /usr/share/nginx/html;
 }
}
➜

NodeJS代码如下

const express = require('express');

const port = 3000;
const host = '127.0.0.1';
const options = { };

const app = express();

app.get('/', (req, res) => {
 res.status(200)
 .json(`Hello ${req.header("ssl_client")}, your certificate was issued by ${req.header("SSL_Client_Issuer")}!`);
});
app.listen(port, host, () => {
 console.log("listening");
})

使用curl测试一下便会输出客户端DN。

$ curl --cert user1.crt --key user1.key https://mtls.example.com/
"Hello emailAddress=user1@example,CN=exmaple,OU=server,C=exmaple, your certificate was issued by emailAddress=user1@example,CN=exmaple,OU=user1,C=exmaple!"

事实上不仅Nginx支持设置客户端认证，Kong网关，云原生应用传输traefik等也早已支持，编程语言层面更是支持开发mTLS应用了。

参考链接：
What is mutual TLS (mTLS)?
Mutual authentication
mTLS Golang Example
How to configure certification based client authentication with Nginx ?
How To Implement Two Way SSL With Nginx
mTLS with node
mTLS with NGINX and NodeJS
LEGO
Firefox导出PFX证书在Win10导入提示密码错误
 NGinx SSL certificate authentication signed by intermediate CA (chain)

双向认证 on 勇气

mTLS 认证