expressjs setting tls connect https nginx server for request - node.js

Question

How can set the request of expressjs to properly identify a TLS connection with https nginx server so that I can perform authentication through getPeerCertificate?
this is my nginx config to transfer request to expressjs api
location /api {
proxy_pass http://10.88.132.14:4337/api;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}

Answer 1

You need to pass the SSL-token and then manually decode it. You pass it through adding X-SSL-CERT with the $ssl_client_escaped_cert. Make sure you are using Nginx 1.13 or later as the $ssl_client_escaped_cert didn't exist in 1.12.
location /api {
proxy_pass http://10.88.132.14:4337/api;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
proxy_set_header X-SSL-CERT $ssl_client_escaped_cert;
}
Now you can't use getPeerCertifice() as this requires the full SSL-connection. Instead you decode the x-ssl-cert header from above using the x509 package:
let cert = req.headers['x-ssl-cert'];
try {
cert = decodeURIComponent(cert);
console.log(x509.getSubject(cert));
} catch (error) {
console.log('Bad SSL-certificate?', error);
}