Simplesmente não inclua um par% tag ca_cert ou ca_path / value no arquivo wpa_supplicant.conf.
Do arquivo wpa_supplicant.conf de exemplo. Observe a terceira frase (ênfase minha):
# ca_cert: File path to CA certificate file (PEM/DER). This file can have one
# or more trusted CA certificates. If ca_cert and ca_path are not
# included, server certificate will not be verified. This is insecure and
# a trusted CA certificate should always be configured when using
# EAP-TLS/TTLS/PEAP. Full path should be used since working directory may
# change when wpa_supplicant is run in the background.