Add other method to handle strings middleware

lib/gitlab/middleware/handle_malformed_strings.rb

@@ -61,7 +61,7 @@ module Gitlab
 
         return false unless credentials
 
-        string_malformed?(credentials)
+        credentials_string_malformed?(credentials)
       end
 
       def param_has_null_byte?(value, depth = 0)
@@ -98,6 +98,13 @@ module Gitlab
         # If we're here, we caught a malformed string. Return true
         true
       end
+
+      def credentials_string_malformed?(string)
+        string.force_encoding('UTF-8').match?(NULL_BYTE_REGEX)
+      rescue ArgumentError, Encoding::UndefinedConversionError
+        # If we're here, we caught a malformed string. Return true
+        true
+      end
     end
   end
 end

spec/lib/gitlab/middleware/handle_malformed_strings_spec.rb

-# frozen_string_literal: true
 
 require 'spec_helper'
 require "rack/test"
@@ -104,6 +103,12 @@ RSpec.describe Gitlab::Middleware::HandleMalformedStrings do
 
       expect(subject.call(env)).not_to eq error_400
     end
+
+    it 'does not reject correct encoded password with special characters' do
+      env = env_for.merge(auth_env("username", "RçKszEwéC5kFnû∆f243fycGu§Gh9ftDj!U", nil))
+
+      expect(subject.call(env)).not_to eq error_400
+    end
   end
 
   context 'in params' do