How can I add an SSL client certificate/key globally in Ubuntu?

I have a web server which requires a client certificate to establish an SSL connection (SSLVerifyClient require in apache). In firefox or chrome, I simply import the .p12-file containing my certificate in PKCS 12 format in the tab "Your Certificates", and this works like it should.

Now I want to use other applications, which afaik don't have the functionality to provide a client SSL certificate themselves (e.g. nautilus). I guess that there has to be a system-wide location where I can store my client certificate, but the only thing I find when googling is where to store CA certificates.

So my question is how can I add SSL client certificate / key files (either .p12 or .crt and .key I guess) so that they are used systemwide?

You would need to install your cert under: /etc/ssl/certs. It would need to have the .crt extension. Your application would need to be configured to look in the /etc/ssl/certs path for the certs, but it should work. I have Fetchmail configured to pull reference /etc/ssl/certs.