[feature request] Client certificate support for TLS authentication

[lescisin]

Hi there - Thanks for all of the excellent work on this project. Really great stuff - I've only been using it for about a week and already it's been helpful for me. I especially appreciate the simplicity of posting messages - it makes it so easy to integrate into other services.

My suggestion:

I was hoping to use client certificates on my front end proxy for TLS authentication to ntfy. I configured my proxy for this and I'm able to authenticate and then access ntfy via browser - I get prompted for the client cert and all works. (hooray!) However, doing the same on the android app, I get the error below.

I'm thinking that the client Android app does not support client certificates based on this. I am submitting this suggestion in hopes that the feature might be considered as a future enhancement.

[kk7ds]

I would really like this as well! I use user cert auth for everything (related to my automation systems) and it's definitely be preferable to be able to do that for ntfy as well instead of having to have a separate scheme.