TLS Mutual Authentication between squid transparent proxy and external endpoint

Hello,

Mutual TLS (mTLS) authentication is a two-way authentication process where both the client (Squid proxy in your case) and the server verify each other’s identities before establishing a secure communication channel. In order to set this up, you would typically require certificates for both parties.

Here are the general steps you should follow to configure mTLS with Squid.

Step 1: Obtain a client certificate for Squid.

This client certificate, typically issued by a trusted certificate authority (CA), is used to authenticate the Squid proxy to the external server. You need to install this certificate on your Squid server.

Step 2: Configure Squid to use the client certificate.

Once you’ve obtained the certificate, you can configure Squid to use it for all outgoing connections. In your Squid configuration file (/etc/squid/squid.conf), add these lines:

# Path to the client certificate
sslcert=/path/to/your/client/cert.pem

# Path to the private key for the client certificate
sslkey=/path/to/your/private/key.pem

You may also need to specify the path to the CA certificate:

sslflags=DONT_VERIFY_PEER
sslproxy_cert_error allow all
sslproxy_flags DONT_VERIFY_PEER
sslproxy_cafile /path/to/ca/cert.pem

Replace /path/to/your/client/cert.pem, /path/to/your/private/key.pem, and /path/to/ca/cert.pem with the actual paths to your certificate, private key, and CA certificate files respectively.

Step 3: Reload Squid.

Finally, reload Squid to apply the changes:

sudo systemctl reload squid

Please note that actual steps can vary based on Squid version, OS version, and the specific setup of your infrastructure. It’s recommended to refer to the official Squid documentation and the documentation of your OS for more accurate information.

This setup assumes that the external endpoint server is already configured for mutual TLS authentication. If it’s not, you would need to configure it similarly: install a server certificate, and configure it to require and verify client certificates.

Lastly, please ensure that you secure the private keys properly and restrict their access, as they can be used to impersonate your server or client.