If I try to add it from that plugin I get
There was an error while trying to import the private key and signed certificate. Internal server error: No certificate was found in the input.
Use the form below to import a private key and certificate that was provided by a Certificate Authority. Make sure that root certificates of the CA signing the certificate are present in the truststore. Otherwise you will need to manually import them using the “keytool” command line tool. If you are seeing errors related to “Invalid key size” you might need to install “Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files”