A and C:
For the explicit proxy method, the request contains the destination IP address of the configured proxy and the client browser sends requests to the proxy directly. You can use one of following methods to authenticate users with the explicit proxy:
Kerberos, which requires a web proxy license.
SAML 2.0, which requires Panorama, a Prisma Access license, the Cloud Services 3.2.1 plugin (and later versions), and the add-on web proxy license.
Cloud Identity Engine, which requires Panorama, a Prisma Access license, the Cloud Services 3.2.1 plugin (and later versions), and the add-on web proxy license.
https://docs.paloaltonetworks.com/pan-os/11-0/pan-os-new-features/networking-features/web-proxy#id3d1ea0dd-360f-44ee-8c48-30678c80d509_id2b5c6385-2ec6-4ba8-b1f1-2bea8b5139f5