How do I install the OWASP ZAP certificate as a trusted system CA on Bluestacks? I have a rooted bluestacks android. I would like to use ZAP to monitor its SSL traffic.

I exported ZAP's SSL certificate as a .cer file ("----- BEGIN CERTIFICATE .... ------ END CERTIFICATE -------"). Now I wish to imported this certificate into bluestacks. 

The way I found was using an apk called "Root Certificate Manager". However, when I try to import the .cer file I get an error response saying the ".cer" extension isn't supported. 

I guess I need to convert it but I can't find the right format to convert to.
So, I found the solution and it's a little dumb / a little funny. It seems that "Root Certificate Manager" is able to import the same .cer file if it placed in the device's storage. I guess they have a bug in their "import from windows" functionality.