adolf@175-181-175-239 ~ $ gnutls-cli -p 8080 radio.mcu.edu.tw
Processed 137 CA certificate(s).
Resolving 'radio.mcu.edu.tw:8080'...
Connecting to '120.96.120.172:8080'...
- Certificate type: X.509
- Got a certificate list of 1 certificates.
- Certificate[0] info:
 - subject `CN=radio.mcu.edu.tw', issuer `CN=Let's Encrypt Authority X3,O=Let's Encrypt,C=US', serial 0x03d590578053df43b5350a79ba3ab67749db, RSA key 2048 bits, signed using RSA-SHA256, activated `2019-11-03 11:59:56 UTC', expires `2020-02-01 11:59:56 UTC', pin-sha256="LfxVEjGA0adX50c51YIAElg2gZ7WZDZDOK+GbJHSQf4="
	Public Key ID:
		sha1:ce12730c607099b8535ee64dcdc6128f32c94f26
		sha256:2dfc55123180d1a757e74739d58200125836819ed664364338af866c91d241fe
	Public Key PIN:
		pin-sha256:LfxVEjGA0adX50c51YIAElg2gZ7WZDZDOK+GbJHSQf4=

- Status: The certificate is NOT trusted. The certificate issuer is unknown.
*** PKI verification of server certificate failed...
*** Fatal error: Error in the certificate.