A utility library for automating Firefox' mTLS host:certificate preference assignment file (ClientAuthRememberList.bin).

This should be paired with policies.json certificate configuration management as per Firefox policy-templates, particularly a Certificates -> Install stanza for filesystem resident certs and/or a SecurityDevices stanza for PKCS#11 resident certs.

For its configuration, FF-CARL currently requires x509 client certificates to be in DER format. The library will issue an io::Error if the certificate bytes are not that of DER encoding, or if the DER certificate is otherwise unable to be parsed. Please be aware that the DER certificate being used for configuration doesn't need to be the very same certificate known to Firefox, just a DER encoded version of it!

Pull in the lib using your Cargo.toml file:

[dependencies]
ff-carl = "1.0.2"

Or simply

cargo add ff-carl

And run an example (being sure to appropriately substitute filesystem paths):

use ff_carl::write_entry;
use ff_carl::EntryArgs;
use std::path::PathBuf;

fn main() -> Result<(), std::io::Error> {
     let der_cert = std::fs::read("/path/to/cert.der").expect("Failed to read certificate.");
     let entry_args = EntryArgs::new(
         "https", // scheme
         "mtls.cert-demo.com", // ascii_host
         443, // port
         "cert-demo.com", // base_domain
         der_cert.as_ref(), // DER cert byte array
     )?;

     let backing_path = PathBuf::from("/path/to/firefox/profile/ClientAuthRememberList.bin");

     write_entry(entry_args, backing_path)
}

To write multiple host:certificate ClientAuthRememberList Entry values, use the ff_carl::write_entries function.