Apache NiFi Toolkit
Also available as:

TLS Generation Toolkit

In order to facilitate the secure setup of NiFi, you can use the tls-toolkit command line utility to automatically generate the required keystores, truststore, and relevant configuration files. This is especially useful for securing multiple NiFi nodes, which can be a tedious and error-prone process.

Wildcard certificates (i.e. two nodes node1.nifi.apache.org and node2.nifi.apache.org being assigned the same certificate with a CN or SAN entry of *.nifi.apache.org) are not officially supported and not recommended. There are numerous disadvantages to using wildcard certificates, and a cluster working with wildcard certificates has occurred in previous versions out of lucky accidents, not intentional support. Wildcard SAN entries are acceptable if each cert maintains an additional unique SAN entry and CN entry.