opensslコマンドを利用して、サーバーに設定されている証明書情報を確認する方法

## 始めに
opensslコマンドを利用して、サーバーに設定された証明書情報を確認する方法をまとめます。

## コマンド
`openssl s_client -connect ssl.example.org:443 -showcerts < /dev/null`

## 返り値の例
* 1つ目の証明書はサーバー証明書、2つ目は中間証明書。
* `Certificate chain` の頭にsが付いている行が証明書情報、iの行が発行者の情報
  * 証明書情報のCN = Common Name

```shell-session
$ openssl s_client -connect github.com:443 -showcerts < /dev/null
CONNECTED(00000003)
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert High Assurance EV Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 Extended Validation Server CA
verify return:1
depth=0 businessCategory = Private Organization, jurisdictionC = US, jurisdictionST = Delaware, serialNumber = 5157550, street = "88 Colin P Kelly, Jr Street", postalCode = 94107, C = US, ST = California, L = San Francisco, O = "GitHub, Inc.", CN = github.com
verify return:1
---
Certificate chain
 0 s:/businessCategory=Private Organization/jurisdictionC=US/jurisdictionST=Delaware/serialNumber=5157550/street=88 Colin P Kelly, Jr Street/postalCode=94107/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=github.com
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
 1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=/businessCategory=Private Organization/jurisdictionC=US/jurisdictionST=Delaware/serialNumber=5157550/street=88 Colin P Kelly, Jr Street/postalCode=94107/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=github.com
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
---
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 3637 bytes and written 434 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: 2850806DDE9DCDB9F5DB4EEBCF2752BDA9DC7244907677EE6BDE6F401D76D67E
    Session-ID-ctx:
    Master-Key: 3DD6FE32CA6D5FDDACBC48465CB200FFF894C4601B978F7A666F3C72ECED6FA9D8745EECC3C3CD17C3C1149933B6582C
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1490110988
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
DONE
```

## 参考
* [opensslコマンドで証明書情報を確認したい。 │ サポート │ GMOグローバルサイン](https://jp.globalsign.com/support/faq/07.html)