RUBY-3832 Raise on invalid tls/ssl boolean URI option

lib/mongo/uri.rb

@@ -503,6 +503,12 @@ def validate_uri_options!
       # 'tls' and 'ssl'. In order to fulfill this, we parse the values of each instance into an
       # array; assuming all values in the array are the same, we replace the array with that value.
       unless uri_options[:ssl].nil? || uri_options[:ssl].empty?
+        # A nil element means an invalid value (e.g. tls=yes) was supplied.
+        # Refuse it rather than silently connecting over plaintext (RUBY-3832).
+        if uri_options[:ssl].include?(nil)
+          raise_invalid_error_no_fmt!("invalid boolean value for 'tls' or 'ssl'; only 'true' and 'false' are accepted")
+        end
+
         unless uri_options[:ssl].uniq.length == 1
           raise_invalid_error_no_fmt!("all instances of 'tls' and 'ssl' must have the same value")
         end

lib/mongo/uri/options_mapper.rb

@@ -354,13 +354,25 @@ def stringify_bool(value)
 
       # Converts the value into a boolean and returns it wrapped in an array.
       #
-      # @param [ String ] name Name of the URI option being processed.
+      # tls and ssl are the only repeated_bool options. An invalid value is
+      # preserved as a nil element rather than warned-and-dropped, so that
+      # URI#validate_uri_options! can detect it and raise instead of silently
+      # falling back to a plaintext connection (RUBY-3832).
+      #
+      # @param [ String ] _name Name of the URI option being processed.
       # @param [ String ] value URI option value.
       #
-      # @return [ Array<true | false> | nil ] The boolean value parsed and wraped
-      #   in an array.
-      def convert_repeated_bool(name, value)
-        [ convert_bool(name, value) ]
+      # @return [ Array<true | false | nil> ] The boolean value parsed and
+      #   wrapped in an array.
+      def convert_repeated_bool(_name, value)
+        case value
+        when true, 'true', 'TRUE'
+          [ true ]
+        when false, 'false', 'FALSE'
+          [ false ]
+        else
+          [ nil ]
+        end
       end
 
       # Reverts a repeated boolean type.

spec/mongo/uri_option_parsing_spec.rb

@@ -102,6 +102,21 @@
     end
   end
 
+  # TLS boolean options must fail loudly on an invalid value: an unrecognized
+  # value such as 'yes' or '1' would otherwise be discarded and the connection
+  # would silently fall back to plaintext (RUBY-3832).
+  shared_examples_for 'a strict boolean option' do
+    it_behaves_like 'a boolean option'
+
+    %w[ yes no 1 0 on off invalid ].each do |bad_value|
+      context "is #{bad_value}" do
+        let(:string) { "mongodb://example.com/?#{uri_option}=#{bad_value}" }
+
+        it_behaves_like 'raises parse error'
+      end
+    end
+  end
+
   shared_examples_for 'an inverted boolean option' do
     let(:string) { "mongodb://example.com/?#{uri_option}=true" }
 
@@ -460,14 +475,14 @@
     let(:uri_option) { 'ssl' }
     let(:ruby_option) { :ssl }
 
-    it_behaves_like 'a boolean option'
+    it_behaves_like 'a strict boolean option'
   end
 
   context 'tls' do
     let(:uri_option) { 'tls' }
     let(:ruby_option) { :ssl }
 
-    it_behaves_like 'a boolean option'
+    it_behaves_like 'a strict boolean option'
   end
 
   context 'tlsAllowInvalidCertificates' do