TF-8697: Support Ruby versions lacking OpenSSL constant (#300)

* Support ruby 2.3

This restores support for much older versions of ruby such as 2.3. While
these versions are EOL'd, they do still appear in usage in things like
embedded chef. It's not a big change to restore functionality, so we've
done that.

* Update changelog and version number

---------

Co-authored-by: Evan Phoenix <evan@phx.io>

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 ## v?.??.? (Unreleased)
 
+## v0.18.1 (September 14, 2023)
+
+BUG FIXES
+
+- Restored the ability to use this gem with older Ruby versions that do not have
+  the `OpenSSL::SSL::TLS1_2_VERSION` constant.
+
 ## v0.18.0 (September 14, 2023)
 
 IMPROVEMENTS

lib/vault/client.rb

@@ -64,6 +64,13 @@ class Client
       a << PersistentHTTP::Error
     end.freeze
 
+    # Vault requires at least TLS1.2
+    MIN_TLS_VERSION = if defined? OpenSSL::SSL::TLS1_2_VERSION
+                        OpenSSL::SSL::TLS1_2_VERSION
+                      else
+                        "TLSv1_2"
+                      end
+
     include Vault::Configurable
 
     # Create a new Client with the given options. Any options given take
@@ -112,8 +119,7 @@ def pool
 
         @nhp.verify_mode = OpenSSL::SSL::VERIFY_PEER
 
-        # Vault requires at least TLS1.2
-        @nhp.min_version = OpenSSL::SSL::TLS1_2_VERSION
+        @nhp.min_version = MIN_TLS_VERSION
 
         # Only use secure ciphers
         @nhp.ciphers = ssl_ciphers

lib/vault/persistent.rb

@@ -1043,7 +1043,15 @@ def ssl connection
     connection.use_ssl = true
 
     connection.ciphers     = @ciphers     if @ciphers
-    connection.min_version = @min_version if @min_version
+
+    if @min_version
+      if connection.respond_to? :min_version=
+        connection.min_version = @min_version
+      else
+        connection.ssl_version = @min_version
+      end
+    end
+
     connection.ssl_timeout = @ssl_timeout if @ssl_timeout
 
     connection.verify_depth = @verify_depth

lib/vault/version.rb

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: MPL-2.0
 
 module Vault
-  VERSION = "0.18.0"
+  VERSION = "0.18.1"
 end