网站ssl证书怎么查

openssl s_client -connect example.com:443 -servername example.com

CONNECTED(00000003)
...
SSL handshake has read 3439 bytes and written 443 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
    ...
    Subject Public Key Info:
        Public Key Algorithm: rsaEncryption
        RSA Public Key: (2048 bit)
            ...
    X509v3 extensions:
        X509v3 Subject Alternative Name:
            DNS:example.com
        X509v3 Basic Constraints:
            CA:FALSE
        X509v3 Key Usage:
            Digital Signature, Key Encipherment
        X509v3 Extended Key Usage:
            TLS Web Server Authentication
        X509v3 Certificate Policies:
            Policy: 2.23.140.1.2.1
              ...
        Authority Information Access:
            OCSP - URI:http://ocsp.example.com
            CA Issuers - URI:http://ca.example.com/cert.crt
        ...
---