The following already works:
* Custom key sizes, e.g. 2048 bits
* Custom key types, e.g. ECC
* Multiple trusted root CAs in `/var/lib/icinga2/certs/ca.crt`
* Different root CAs per cluster subtree, as long as each node trusts the
issuers of the certificates of all nodes it's directly connected to
* Any number of intermediate CAs
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