Simply don't include a ca_cert
or ca_path
tag/value pair in the wpa_supplicant.conf file.
From the example wpa_supplicant.conf file. Note the third sentence (emphasis mine):
# 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.