# Certifix

Not an Asterix character.  A small HTTP(S)[*] API that accepts X509
CSRs and signs them if they contain the magic number (specifically, if
they have a custom `challengePassword` attribute containing a
pre-agreed value)

Modelled on the Puppet CA "Policy-based autosigning" functionality,
but without the rest of Puppet

What's it for? I have a bunch of small devices on my LAN that may or
may not be able to retain persistent state across reboots. I would
like them to be able to talk securely to a server using standard TLS
with client authentication, and without having to rely on network
firewall rules to prevent the rest of the world also talking to the
service.

[*] it will do S, but as of writing this footnote it doesn't yet

## To try it out

_This is experiment-quality code that I have published mostly so that
it does't die with my laptop. Some day it will be grown-up but in the
meantime try it at your own risk - or even better, don't try it_

It's written in [Fennel](https://www.fennel-lang.org). To build it
either use Nix or read [package.nix](package.nix) and figure out how
to replicate the steps manually.  Note that it requires a patch to the
luaossl module


```
# pick a PSK
echo 'loves labours lost' > psk
chmod 0700 psk

# create CA key and cert used for signing
openssl genrsa -out ca.key 4096
CN=CA openssl req -config openssl.cnf -x509 -new -nodes -key ca.key -sha256 -days 3650  -out ca.crt

# create key for the server and sign it with the CA 
CN=localhost openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout server.key --out server.csr
openssl x509 -req -in server.csr -days 365 -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt

# create example client CSR for testing (check openssl.cnf against "psk" file)
CN=rotuer openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout client.key -out client.csr

# build and start the server
nix-build && result/bin/certifix  --challenge-password psk  --certificate ca.crt --private-key ca.key localhost:19613

# send it
curl -v -H 'content-type: application/x-pem-file' --data-binary @client.csr  https://localhost:19613/sign
```

## Background

* [how Puppet does it](https://www.puppet.com/docs/puppet/7/ssl_attributes_extensions#csr_custom_attributes-recommended-oids-custom-attributes)

* [RFC 5967 - spec for a CSR](https://datatracker.ietf.org/doc/html/rfc5967)