wpa_supplicant slow to verify server certificate

[wpa at fastmail.fm]

I check the time of each EAP messages coming into the supplicant, and
the time of the EAP messages going out of the supplicant. For all other
messages, the time difference between EAP REQ and EAP RSP is about 0.1
to 0.2 second, but for the certificate verification, the last EAP RSP
message is about 1.5 seconds from the time EAP REQ comes in. The openssl
was used with the supplicant. Maybe the openssl is causing the delay in
verifying the certificate, but I don't know how to improve the time to
verify the server certificate.

Thanks.