How to view the server certificate using the OpenSSL "s_client -connect" command?

You can get the server certificate, if use "s_client -connect" without the "-quiet" option as shown below:

C:\Users\fyicenter>\local\openssl\openssl.exe

OpenSSL> s_client -connect www.twitter.com:443

CONNECTED(0000015C)
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert 
SHA2 Extended Validation Server CA
verify error:num=20:unable to get local issuer certificate
---
Certificate chain
 0 s:/businessCategory=Private Organization/jurisdictionC=US/jurisdictionST=Delaware
   /serialNumber=4337446/street=Suite 900/street=1355 Market St/postalCode=94103
   /C=US/ST=California/L=San Francisco/O=Twitter, Inc./OU=Twitter Security/CN=twitter.com
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
 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
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/businessCategory=Private Organization/jurisdictionC=US/jurisdictionST=Delaware
   /serialNumber=4337446/street=Suite 900/street=1355 Market St/postalCode=94103
   /C=US/ST=California/L=San Francisco/O=Twitter, Inc./OU=Twitter Security/CN=twitter.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 3825 bytes and written 433 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: 71EB0BD6387EC907A83503D40108C062D9738D7243D39EAAF90ACA380380C297

    Session-ID-ctx:
    Master-Key: 29B91AACC05EC380AB10412891BFCB21FD6243BDC891A43D3FC2C502CBFF4D3C
683ADB2996912ACF31FBD8F57A38F07D
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 129600 (seconds)
    TLS session ticket:
    0000 - 66 03 db e6 37 8d d7 17-63 3a ab ff a4 a0 b0 59   
    0010 - ae a1 b4 51 24 e3 49 14-78 15 f5 42 7d dc b9 06   
    0020 - ca bd 81 ad c4 29 27 29-27 3c 9f a9 69 e6 6c 0e   
    0030 - 44 eb 96 3a 6d d2 60 c1-32 f9 db 6e a8 c5 e5 24   
    0040 - 40 d1 ee 82 cb 19 69 c5-1b 00 78 b7 ff 54 2c fc   
    0050 - 3c 6d f1 f3 f4 90 02 bb-45 f0 97 2e 69 80 e3 e4   
    0060 - 93 dd 5d 3b 47 9b b6 de-b0 a6 a2 21 84 5b 2c 41   
    0070 - 5f 1a 84 1d ea 82 48 14-7b 4f 98 dd 40 f9 e4 26   
    0080 - bb 96 e4 8e 9d 28 d7 ae-02 5f ce 80 5c 75 ae 38   
    0090 - 8b 52 da db 22 bb 3f 0f-0a 28 20 4e 4b b0 2c e4   

    Start Time: 1469966886
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
---
closed

What you are getting from the output:

• The server certificate between "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----" lines.
• The server certificate chain information. There are 3 certificates in the chain. The last certificate is issued by "/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification Authority"
• The server public key size is 2048 bit long.
• The protocol used to secure the connection is "TLSv1.2".

⇒ Save OpenSSL Command Output to File

⇐ OpenSSL "s_client -connect" - Connect to HTTPS Web Site

⇑ OpenSSL "s_client" Command

⇑⇑ OpenSSL Tutorials