HTTP authentication credential leak to target websites in scrapy

Scrapy is a high-level web crawling and scraping framework for Python. If you use `HttpAuthMiddleware` (i.e. the `http_user` and `http_pass` spider attributes) for HTTP authentication, all requests will expose your credentials to the request target. This includes requests generated by Scrapy components, such as `robots.txt` requests sent by Scrapy when the `ROBOTSTXT_OBEY` setting is set to `True`, or as requests reached through redirects. Upgrade to Scrapy 2.5.1 and use the new `http_auth_domain` spider attribute to control which domains are allowed to receive the configured HTTP authentication credentials. If you are using Scrapy 1.8 or a lower version, and upgrading to Scrapy 2.5.1 is not an option, you may upgrade to Scrapy 1.8.1 instead. If you cannot upgrade, set your HTTP authentication credentials on a per-request basis, using for example the `w3lib.http.basic_auth_header` function to convert your credentials into a value that you can assign to the `Authorization` header of your request, instead of defining your credentials globally using `HttpAuthMiddleware`.