HPR3338: Using openssl s_client like telnet

Connect to port 443 and send some HTTP signals:

$ openssl s_client -connect example.com:443
[...snip...]
Verify return code: 0 (ok)
Extended master secret: no
Max Early Data: 0
---

You're now connected. If you wait too long, your connection will likely time out.
View the default landing page of the site you've connected with:

GET / HTTP/1.1
HOST: example.com

In return, you get a dump of the HTML source of the default page (usually index.html) in your terminal.

You can also use OpenSSL s_client for email servers using SSL.
Before you can send credentials, you must encode your email username and passphrase into Base64. The easiest method I know is this Perl one-liner:

$ perl -MMIME::Base64 -e 'print encode_base64("myUserName");'
$ perl -MMIME::Base64 -e 'print encode_base64("myPassPhrase");'

Take note of the results.

The s_client session, aside from authentication, is basically the same as a telnet session. You can find good telnet tutorials all over the Internet, and aside from sending your credentials, they apply to s_client.

Here's a copy-paste of an example session:

$ openssl s_client -starttls smtp -connect email.example.com:587
> ehlo example.com
> auth login
##paste your user base64 string here####
##paste your password base64 string here####

> mail from: [email protected]
> rcpt to: [email protected]
> data
> Subject: Test 001
This is a test email.
.
> quit