Client-side SSL

For excessively paranoid client authentication.

Using self-signed certificate.

Create a Certificate Authority root (which represents this server)

Organization & Common Name: Some human identifier for this server CA.

openssl genrsa -des3 -out ca.key 4096
openssl req -new -x509 -days 365 -key ca.key -out ca.crt

Create the Client Key and CSR

Organization & Common Name = Person name

openssl genrsa -des3 -out client.key 4096
openssl req -new -key client.key -out client.csr
# self-signed
openssl x509 -req -days 365 -in client.csr -CA ca.crt -CAkey ca.key -set_serial 01 -out client.crt

Convert Client Key to PKCS

So that it may be installed in most browsers.

openssl pkcs12 -export -clcerts -in client.crt -inkey client.key -out client.p12

Convert Client Key to (combined) PEM

Combines client.crt and client.key into a single PEM file for programs using openssl.

openssl pkcs12 -in client.p12 -out client.pem -clcerts

Install Client Key on client device (OS or browser)

Use client.p12. Actual instructions vary.

Install CA cert on nginx

So that the Web server knows to ask for (and validate) a user's Client Key against the internal CA certificate.

ssl_client_certificate /path/to/ca.crt;
ssl_verify_client optional; # or `on` if you require client key

Configure nginx to pass the authentication data to the backend application:

• Client Side Certificate Auth in Nginx, section “Passing to PHP.”
• SSL module documentation

Using CACert Keys

• Get client key from CACert
• Install client key in client device.
• Install CACert root certs in server and client device.
• Configure nginx, as above.