avoid reusing generic validation method during params securization

Fixes #4952

logstash-core/lib/logstash/config/mixin.rb

@@ -144,7 +144,7 @@ def config_init(params)
 
     # now that we know the parameters are valid, we can obfuscate the original copy
     # of the parameters before storing them as an instance variable
-    self.class.validate_check_parameter_values(original_params)
+    self.class.secure_params!(original_params)
     @original_params = original_params
 
     @config = params
@@ -542,6 +542,14 @@ def validate_value(value, validator)
       return true, result
     end # def validate_value
 
+    def secure_params!(params)
+      params.each do |key, value|
+        if @config[key][:validate] == :password && !value.is_a?(::LogStash::Util::Password)
+          params[key] = ::LogStash::Util::Password.new(value)
+        end
+      end
+    end
+
     def hash_or_array(value)
       if !value.is_a?(Hash)
         value = [*value] # coerce scalar to array if necessary