A Complete Guide to Securely Connecting Nginx and Go Using Mutual TLS
How to use TLS, client authentication, and CA certificates in Nginx and Go
Create a private key and request a certificate for your Nginx server
Before you can teach your server to speak TLS, you will need a certificate issued by a trusted certificate authority (CA). If your organization already runs its own CA and you have a private key and certificate for your Nginx server, along with your CA's root certificate, you can skip to the next step.
To request a certificate from your CA using the step CLI, bootstrap your CA with step ca bootstrap and run the following command (sub the server name for the actual name / DNS name of your Nginx server).
$ step ca certificate "myserver.internal.net" server.crt server.keyYour certificate and private key will be saved in server.crt and server.key respectively.
Request a copy of your CA root certificate, which will be used to make sure each application can trust certificates presented by other applications.
$ step ca root ca.crtYour certificate will be saved in ca.crt.
Configure Nginx to authenticate itself with its TLS certificate
We now want to instruct our Nginx server to identify itself using the certificate issued in the last step and to force clients to connect over TLS.
In your Nginx configuration's server block, enable ssl for the listening socket and specify the locations of the server's certificate and private key. We'll also tell Nginx to use TLS protocols and our preferred ciphers:
server {
listen 443 ssl;
server_name myserver.internal.net;
ssl_certificate server.crt;
ssl_certificate_key server.key;
ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers HIGH:!aNULL:!MD5;
# ...
}Configure Nginx to require clients to authenticate with a certificate issued by your CA
To tell Nginx to use mutual TLS and not just one-way TLS, we must instruct it to require client authentication to ensure clients present a certificate from our CA when they connect.
In your server's configuration block, specify the location of your CA root certificate to use for authenticating client certificates. You may choose to make client verification optional so your application can return a 403 message:
server {
listen 443 ssl;
server_name myserver.internal.net;
# ...
ssl_client_certificate /etc/nginx/client_certs/ca.crt;
ssl_verify_client optional;
# ...
location / {
if ($ssl_client_verify != SUCCESS) {
return 403;
}
# ...
}Read more
That's it! Nginx should now be able to receive TLS connections from clients who authenticate themselves using a certificate issued by your trusted CA.
Create a private key and request a certificate for your Go client
Request a new certificate from your CA to represent your Go client.
$ step ca certificate "myuser" client.crt client.keyYour certificate and private key will be saved in client.crt and client.key respectively.
Make a request from Go using mutual TLS
Now, we need only to configure our Go client to make authenticated requests using our certificate and private key. The CA root certificate will be used to verify that the client can trust the certificate presented by the server.
In your Go code, we specify a TLS stack configuration for your client(s) making requests. The configuration includes 1.) root certificates of all trusted CAs for verification of the server's certificate in a pool we create. And 2.) the client's own certificate and private key for server-side client certificate verification.
// ...
caCert, _ := ioutil.ReadFile("ca.crt")
caCertPool := x509.NewCertPool()
caCertPool.AppendCertsFromPEM(caCert)
cert, _ := tls.LoadX509KeyPair("client.crt", "client.key")
client := &http.Client{
Transport: &http.Transport{
TLSClientConfig: &tls.Config{
RootCAs: caCertPool,
Certificates: []tls.Certificate{cert},
},
},
}
// Make a request
r, err := client.Get("https://myserver.internal.net:443")
// ...Read more
Automate certificate renewal
By default, step-ca issues certificates with a 24 hour expiration. Short-lived certificates have many benefits but also require that you renew your certificates each day before they expire. How you renew certificates is often dependent on how you deploy your application. See the step-ca certificate lifecycle management docs for more information.
All documentation content from the Hello mTLS project is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).
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