I installed pnp for Icingaweb2 here: https://exchange.icinga.org/icinga/PNP (for the frontend) and installed pnp4nagios from the instructions here: (which is necessary for the pnp module to work).
I followed all the instructions from the docs, including these steps:
1. enabled icinga2 feature "perfdata"
2. enabled httpd service
3. edited /etc/pnp4nagios/npcd.cfg file to have user as "icinga" and group as "icinga", as well as changing the perfdata_spool_dir to equal "/var/spool/icinga2/perfdata"
4. enabled npcd service
5. edited /etc/httpd/conf.d/pnp4nagios.conf to change AuthUserFile path to "/etc/nagios/passwd"
6. changed user and pass (presumably) in that file to "icingaadmin:<MYPASSWORD>" from "nagiosadmin:<defaultpass>"
7. changed ownership of /var/lib/pnp4nagios/ folder to icinga using the command "chown -R icinga.icinga /var/lib/pnp4nagios/"
Thanks so much!