~ > openssl s_client -connect slack.com:443
CONNECTED(00000003)
depth=1 C = US, ST = California, L = Sunnyvale, O = Fortinet, OU = Certificate Authority, CN = FortiGate CA, emailAddress = support@fortinet.com
verify error:num=19:self signed certificate in certificate chain
---
Certificate chain
 0 s:/C=US/ST=California/L=San Francisco/O=Slack Technologies, Inc/CN=*.slack.com
   i:/C=US/ST=California/L=Sunnyvale/O=Fortinet/OU=Certificate Authority/CN=FortiGate CA/emailAddress=support@fortinet.com
 1 s:/C=US/ST=California/L=Sunnyvale/O=Fortinet/OU=Certificate Authority/CN=FortiGate CA/emailAddress=support@fortinet.com
   i:/C=US/ST=California/L=Sunnyvale/O=Fortinet/OU=Certificate Authority/CN=FortiGate CA/emailAddress=support@fortinet.com
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=US/ST=California/L=San Francisco/O=Slack Technologies, Inc/CN=*.slack.com
issuer=/C=US/ST=California/L=Sunnyvale/O=Fortinet/OU=Certificate Authority/CN=FortiGate CA/emailAddress=support@fortinet.com
---
No client certificate CA names sent
---
SSL handshake has read 2274 bytes and written 636 bytes
---
New, TLSv1/SSLv3, Cipher is AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : AES256-GCM-SHA384
    Session-ID: B0A7F33109DA55B49106A8ADE4F44AEDB29170DAD92F20ED9640819321CDC7A8
    Session-ID-ctx:
    Master-Key: C9700C35900890BE764F169B3F1D14A0C756D831E97A8F97691DC8470BA57CA9A3DC97DAD0E26B42DC73900DE4BEEADF
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 300 (seconds)
    TLS session ticket:
    0000 - 42 24 b7 9b 4d 7a 60 ba-fd 7a fe 51 2d b4 c0 60   B$..Mz`..z.Q-..`
    0010 - ad 53 45 e4 07 44 98 03-47 c3 fd ac 77 99 75 37   .SE..D..G...w.u7
    0020 - 77 35 e2 bc 9c 0d 75 7b-55 f9 a4 66 a1 37 cd 92   w5....u{U..f.7..
    0030 - 88 99 12 90 16 2a 46 69-5a 9e 61 d4 57 35 fe 84   .....*FiZ.a.W5..
    0040 - b5 3b 2b c8 3f 00 b7 48-29 34 5a c6 82 34 4d b1   .;+.?..H)4Z..4M.
    0050 - 3d eb 95 99 a0 c0 02 a5-2d 6d fe 99 96 42 08 8f   =.......-m...B..
    0060 - d2 0f f9 4b b4 54 cf 59-f6 98 46 db e6 81 83 53   ...K.T.Y..F....S
    0070 - 51 cb 59 6b 18 2d 61 12-5c 95 07 3d 1b cb f1 74   Q.Yk.-a.\..=...t
    0080 - 5f f4 0c 6f d9 c6 64 6d-e5 c7 d6 de 73 e9 f3 d7   _..o..dm....s...
    0090 - ac 29 66 0d 77 95 af b6-0e 1b 04 a2 95 a5 c8 e4   .)f.w...........

    Start Time: 1449439346
    Timeout   : 300 (sec)
    Verify return code: 19 (self signed certificate in certificate chain)
---
^C