Firewall flex credits and authcodes are used to license VM-Series firewalls. The methods for using authcodes during bootstrapping include:

A. /config/bootstrap.xml file of complete bootstrapping package: The bootstrap.xml file is a key component of the bootstrapping process. It can contain the authcode for licensing.

B. /license/authcodes file of complete bootstrap package: A dedicated authcodes file within the bootstrap package is another valid method for providing license information.

C. Panorama device group in Panorama SW Licensing Plugin: While Panorama manages licenses, specifying authcodes directly via a device group is not the typical method for bootstrapping. Panorama usually manages licenses after the firewalls are bootstrapped and connected to Panorama.

D. authcodes= key value pair of Azure Vault configuration: While using Azure Key Vault for storing and retrieving secrets (like authcodes) is a good security practice for ongoing operations, it's not the primary method for initial bootstrapping using flex credits. Bootstrapping typically relies on the local bootstrap package.

E. authcodes= key value pair of basic bootstrapping configuration: This refers to including the authcode directly in the bootstrapping configuration, such as in the init-cfg.txt file or via cloud-init.