Only set min_version on OpenSSL < 1.1.0

Both Red Hat and Debian-like systems configure the minimum TLS version
to be 1.2 by default, but allow users to change this via configs.

On Red Hat and derivatives this happens via crypto-policies[1], which in
writes settings in /etc/crypto-policies/back-ends/opensslcnf.config.
Most notably, it sets TLS.MinProtocol there. For Debian there's
MinProtocol in /etc/ssl/openssl.cnf. Both default to TLSv1.2, which is
considered a secure default.

In constrast, the SSLContext has a hard coded OpenSSL::SSL::TLS1_VERSION
for min_version. TLS 1.0 and 1.1 are considered insecure. By always
setting this in the default parameters, the system wide default can't be
respected, even if a developer wants to.

This takes the approach that's also done for ciphers: it's only set for
OpenSSL < 1.1.0.

[1]: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/security_hardening/using-the-system-wide-cryptographic-policies_security-hardening

Author: ekohl

lib/openssl/ssl.rb

@@ -22,7 +22,6 @@ module OpenSSL
   module SSL
     class SSLContext
       DEFAULT_PARAMS = { # :nodoc:
-        :min_version => OpenSSL::SSL::TLS1_VERSION,
         :verify_mode => OpenSSL::SSL::VERIFY_PEER,
         :verify_hostname => true,
         :options => -> {
@@ -55,6 +54,7 @@ class SSLContext
       if !(OpenSSL::OPENSSL_VERSION.start_with?("OpenSSL") &&
            OpenSSL::OPENSSL_VERSION_NUMBER >= 0x10100000)
         DEFAULT_PARAMS.merge!(
+          min_version: OpenSSL::SSL::TLS1_VERSION,
           ciphers: %w{
             ECDHE-ECDSA-AES128-GCM-SHA256
             ECDHE-RSA-AES128-GCM-SHA256