I am able to do MTLS connections to a given service using curl and httpie. That works fine.

An example of a working httpie command http post --cert=./cert.pem --cert-key=./cert.key <url>
The key is passphrase protected, but I have tried using an unprotected one in Req/elixir and no dice.

But as soon as I try to replicate that in elixir using Req I get errors from the service saying that there is no client certificate being used.

I have tried using certfile and keyfile and password but nothing seems to work and there is remarkably no documentation about this.

I could swear I had it working before but I cannot for the life of me get it working now.

I appreciate this will be reasonably tricky to identify as I cannot obviously share the keys. But I would love any help, I am going slowly insane.