# To authenticate the proxy, 
#you must set the Proxy-Authorization header. 
#You *cannot* use the form http://user:pass@proxy:port 
#in request.meta['proxy']
import base64
proxy_ip_port = "123.456.789.10:8888"
proxy_user_pass = "awesome:dude"
request = Request(url, callback=self.parse)
# Set the location of the proxy
request.meta['proxy'] = "http://%s" % proxy_ip_port
# setup basic authentication for the proxy
encoded_user_pass=base64.encodestring(proxy_user_pass)
request.headers['Proxy-Authorization'] = 'Basic ' + encoded_user_pass