problem with the extention permit-x11-forwarding

[cyber-anon]

Using viper to read the config file, creates a problem with the SSH certificate extension "permit-X11-forwarding" which is converted to lowercase "permit-x11-forwarding" and thus is invalid / unknown.

I do not know how this could be solved.
This seems to be an inherent limitation of viper older than 5 years, and the most common solution people are implementing, is to migrate to another package.

spf13/viper#1014

Since the only case-sensitive extension is this, maybe a solution would be to iterate the Extensions map after being created, and if permit-x11-forwarding is found, modify it with the correct capitalization

[pablo-ruth]

Hi @cyber-anon, sorry for the delay. It's not the most elegant solution, but checking this edge case and fixing it is the simplest way. I've merged the fix and released it here: https://github.com/signmykeyio/signmykey/releases/tag/v0.8.7