Here are the steps used to generate server/client TLS certs/keys for use with NiFi and NiPyAPI.
# use NiFi tls-toolkit to generate CA, server key/cert, client key/cert
./nifi-toolkit-1.4.0/bin/tls-toolkit.sh standalone --certificateAuthorityHostname localhost --hostnames localhost --subjectAlternativeNames nifi,registry,secure-nifi,secure-registry --nifiDnSuffix ", OU=nifi" --keyStorePassword localhostKeystorePassword --trustStorePassword localhostTruststorePassword --clientCertDn "CN=user1, OU=nifi" --clientCertPassword clientPassword --days 9999 --outputDirectory nipyapi-tests
# change to tls-toolkit output directory
cd ./nipyapi-tests
# copy server's key/trust stores
mkdir keys