improve README

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Daniel Barlow 2024-09-25 21:30:32 +01:00
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A small HTTPS API that accepts X509 CSRs and signs them if they
contain the magic number.
Modelled on the Puppet CA "Policy-based autosigning" functionality,
but without the rest of Puppet
[ This README is speculative ]
## Try it out
```
# create CA key and cert
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 client CSR
CN=rotuer openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout client.key -out client.csr
# start the server
bin/certifix
# send it
curl -v -H 'content-type: application/x-pem-file' --data-binary @client.csr http://localhost:8201/sign
```
https://www.puppet.com/docs/puppet/7/ssl_attributes_extensions#csr_custom_attributes-recommended-oids-custom-attributes
Custom attributes can use any public or site-specific OID, with the exception of the OIDs used for core X.509 functionality. This means you cant re-use existing OIDs for things like subject alternative names.
One useful OID is the challengePassword attribute — 1.2.840.113549.1.9.7. This is a rarely-used corner of X.509 that can easily be repurposed to hold a pre-shared key.

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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 'urban cookie collective' > psk
chmod 0700 psk
# create CA key and cert
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 client CSR
CN=rotuer openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout client.key -out client.csr
# start the server
bin/certifix
# send it
curl -v -H 'content-type: application/x-pem-file' --data-binary @client.csr http://localhost:8201/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)