Handling Error Pages in Scrapy

I have one URL in start_urls

The first time the crawler loads the page, it is first shown a 403 error page after which the crawler shuts down.

What I need to do is fill out a captcha on that page and it will then let me access the page. I know how to write the code for bypassing the captcha but where do I put this code in my spider class?

I need to add this on other pages as well when it encounters the same problem.

from scrapy.contrib.spiders import CrawlSpider, Rule
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor

from scrapy.selector import Selector

class MySpider(CrawlSpider):
    name = "myspider"
    allowed_domains = ["mydomain.com"]
    start_urls = ["http://mydomain.com/categories"]
    handle_httpstatus_list = [403] #Where do I now add the captcha bypass code?
    download_delay = 5
    rules = [Rule(SgmlLinkExtractor(allow=()), callback='parse_item')]

    def parse_item (self, response):
        pass