Allow mutual TLS CA to be set using ssl_bind DSL

When using mutual TLS, you must specify the CA certificate chain to use
for verifying the peer. Using Puma's `ssl_bind` DSL did not give you the
option of doing so, which lead to confusing errors when attempting to
use it.

Now, when specifying the `verify_mode` as either `peer` or `force_peer`,
you can use the DSL to set the `ca` value as needed within the `Binder`.
This allows you to use the DSL instead of falling back to the default
`bind` syntax via the URI-style configuration pattern.

lib/puma/dsl.rb

@@ -296,13 +296,14 @@ module Puma
     def ssl_bind(host, port, opts)
       verify = opts.fetch(:verify_mode, 'none')
       no_tlsv1 = opts.fetch(:no_tlsv1, 'false')
+      ca_additions = "&ca=#{opts[:ca]}" if ['peer', 'force_peer'].include?(verify)
 
       if defined?(JRUBY_VERSION)
         keystore_additions = "keystore=#{opts[:keystore]}&keystore-pass=#{opts[:keystore_pass]}"
-        bind "ssl://#{host}:#{port}?cert=#{opts[:cert]}&key=#{opts[:key]}&#{keystore_additions}&verify_mode=#{verify}&no_tlsv1=#{no_tlsv1}"
+        bind "ssl://#{host}:#{port}?cert=#{opts[:cert]}&key=#{opts[:key]}&#{keystore_additions}&verify_mode=#{verify}&no_tlsv1=#{no_tlsv1}#{ca_additions}"
       else
         ssl_cipher_filter = "&ssl_cipher_filter=#{opts[:ssl_cipher_filter]}" if opts[:ssl_cipher_filter]
-        bind "ssl://#{host}:#{port}?cert=#{opts[:cert]}&key=#{opts[:key]}#{ssl_cipher_filter}&verify_mode=#{verify}&no_tlsv1=#{no_tlsv1}"
+        bind "ssl://#{host}:#{port}?cert=#{opts[:cert]}&key=#{opts[:key]}#{ssl_cipher_filter}&verify_mode=#{verify}&no_tlsv1=#{no_tlsv1}#{ca_additions}"
       end
     end
 

test/config/ssl_config.rb

@@ -1,4 +1,13 @@
 key =  File.expand_path "../../examples/puma/puma_keypair.pem", __FILE__
 cert = File.expand_path "../../examples/puma/cert_puma.pem", __FILE__
+ca = File.expand_path "../../examples/puma/client-certs/ca.crt", __FILE__
 
-ssl_bind "0.0.0.0", 9292, :cert => cert, :key => key
+ssl_bind "0.0.0.0", 9292, :cert => cert, :key => key, :verify_mode => "peer", :ca => ca
+
+app do |env|
+  [200, {}, ["embedded app"]]
+end
+
+lowlevel_error_handler do |err|
+  [200, {}, ["error page"]]
+end

test/test_config.rb

@@ -30,6 +30,22 @@ class TestConfigFile < Minitest::Test
     assert_equal [200, {}, ["embedded app"]], app.call({})
   end
 
+  def test_ssl_configuration_from_DSL
+    conf = Puma::Configuration.new do |config|
+      config.load "test/config/ssl_config.rb"
+    end
+
+    conf.load
+
+    bind_configuration = conf.options.file_options[:binds].first
+    app = conf.app
+
+    assert bind_configuration =~ %r{ca=.*ca.crt}
+    assert bind_configuration =~ /verify_mode=peer/
+
+    assert_equal [200, {}, ["embedded app"]], app.call({})
+  end
+
   def test_double_bind_port
     port = (rand(10_000) + 30_000).to_s
     with_env("PORT" => port) do