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Basic SSL Setup - server and client SSL certificate setup

Install nginx on the instance. We would also probably need to install vim as well to make it changes on nginx configuration.

sudo apt update && sudo apt install -y nginx vim
sudo su
mkdir -p /etc/nginx/ssl
cd /etc/nginx/ssl

Create the following file in ca.config. The following ca configuration is used to create and configure SSL certifications

[ ca ]
# `man ca`
default_ca = CA_default

[ CA_default ]
copy_extensions = copy 

[req]
distinguished_name = req_distinguished_name
x509_extensions     = server_cert
req_extensions = server_cert

[req_distinguished_name]
commonName             = commonname

[ v3_ca ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
#authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName          = @alternate_names

[ alternate_names ]
DNS.1       = localhost
DNS.2       = lol.testtest.com

Refer to documentation for more details:
https://jamielinux.com/docs/openssl-certificate-authority/create-the-root-pair.html

openssl genrsa -out ca.key 2048
openssl rsa -in ca.key -pubout > ca.pub

# Certificate "request" but produces a self signed cert instead
openssl req -x509 -config ca.config -new -nodes -key ca.key -sha256 -days 365 -out ca.pem -extensions v3_ca

Create server SSL certificate

openssl genrsa -out dev.app.key.server 2048

# Certificate "request"
# In order to make it easier - use *.example.com for common name
openssl req -new -key dev.app.key.server -out dev.app.csr

openssl x509 -req -in dev.app.csr -CA ca.pem -CAkey ca.key -CAcreateserial -out dev.app.crt.server -days 365 -sha256 -extfile ca.config -extensions server_cert

cp dev.app.crt.server dev.app.crt
cat ca.pem  >> dev.app.crt
cp dev.app.key.server dev.key.crt
cat ca.key  >> dev.key.crt

With that, edit nginx accordingly to allow ssl traffic on the following file /etc/nginx/sites-available/default. Ensure one of the blog have https port, 443 be allowed with ssl and to have the ssl certificate and ssl certificate that we created used here

server {
  listen 443 ssl default_server;
  ssl_certificate     /etc/nginx/ssl/dev.app.crt;
  ssl_certificate_key /etc/nginx/ssl/dev.key.crt;
  ...
}

We can go into another VM instance on Google Compute Engine and try to curl it to the server instance. Copy over the ca.pem over from the server. Google Cloud instances

curl --cacert ca.pem https://instance-1

We would get the following error

curl: (60) SSL: no alternative certificate subject name matches target host name 'instance-1'
More details here: https://curl.haxx.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

Note from above that only 2 domains is acceptable: localhost and lol.testtest.com. Add ip address of the server with the lol.testtest.com domain to the /etc/hosts file.

We can then use curl on domains specified in the SSL Cert - lol.testtest.com to obtain the response accordingly.

curl --cacert ca.pem https://lol.testtest.com

Create client SSL certificate request. We need to pass the certificate request to the instance that has the ca certificate to sign it

openssl genpkey -algorithm RSA -out client.key -pkeyopt rsa_keygen_bits:2048

openssl req -new -key client.key -out client.req -subj /CN=testtest

Sign it and put it back to the caller instance

openssl x509 -req -in client.req -CA ca.pem -CAkey ca.key -set_serial 101 -extensions client -days 365 -sha256 -outform PEM -out client.crt

openssl x509 -in client.crt -noout -text

Adjust nginx configuration - /etc/nginx/nginx.conf

http {
        
        map $ssl_client_s_dn $allowed {
          default no;
          "CN=testtest" yes;
        }

        ...

Adjust the following nginx configuration - /etc/nginx/sites-available/default

server {
        ...

        listen 443 ssl default_server;
        ssl_certificate        /etc/nginx/ssl/dev.app.crt;
        ssl_certificate_key    /etc/nginx/ssl/dev.key.crt;
        ssl_verify_client      on;
        ssl_client_certificate /etc/nginx/ssl/ca.pem;
         
        if ($allowed = "no") {
          return 403;
        }

        ...

We can run curl request

curl --cacert ca.pem https://lol.testtest.com

But we would receive the following response though

<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/1.14.2</center>
</body>
</html>

We would need to pass the client ssl certificates

curl --cacert ca.pem --cert client.crt --key client.key  https://lol.testtest.com