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This is originally my question at stackoverflow.com. (http://stackoverflow.com/q/30511341/3786245) I think it's a bug, so I posted it here.
I'm trying to fetch HTTPS pages through a proxy with digest authentication. Here are my codes:
import urllib.request
class SimplePasswordManager(object):
 def __init__(self, username, password):
 self.username = username
 self.password = password
 def add_password(self, realm, uri, user, passwd):
 pass
 def find_user_password(self, realm, authuri):
 return self.username, self.password
proxy_handler = urllib.request.ProxyHandler({
 'http': '<proxy server ip>',
 'https': '<proxy server ip>',
})
password_mgr = SimplePasswordManager('<username>', '<password>')
proxy_auth_handler = urllib.request.ProxyDigestAuthHandler(passwd=password_mgr)
opener = urllib.request.build_opener(proxy_auth_handler, proxy_handler)
req = opener.open('http://httpbin.org/ip')
print(req.read().decode('ascii'))
req = opener.open('https://httpbin.org/ip')
print(req.read().decode('ascii'))
And the results:
{
 "origin": "<proxy server ip>"
}
Traceback (most recent call last):
 File "/usr/lib/python3.4/urllib/request.py", line 1182, in do_open
 h.request(req.get_method(), req.selector, req.data, headers)
 File "/usr/lib/python3.4/http/client.py", line 1088, in request
 self._send_request(method, url, body, headers)
 File "/usr/lib/python3.4/http/client.py", line 1126, in _send_request
 self.endheaders(body)
 File "/usr/lib/python3.4/http/client.py", line 1084, in endheaders
 self._send_output(message_body)
 File "/usr/lib/python3.4/http/client.py", line 922, in _send_output
 self.send(msg)
 File "/usr/lib/python3.4/http/client.py", line 857, in send
 self.connect()
 File "/usr/lib/python3.4/http/client.py", line 1223, in connect
 super().connect()
 File "/usr/lib/python3.4/http/client.py", line 837, in connect
 self._tunnel()
 File "/usr/lib/python3.4/http/client.py", line 820, in _tunnel
 message.strip()))
OSError: Tunnel connection failed: 407 Proxy Authentication Required
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
 File "proxy_test.py", line 25, in <module>
 req = opener.open('https://httpbin.org/ip')
 File "/usr/lib/python3.4/urllib/request.py", line 463, in open
 response = self._open(req, data)
 File "/usr/lib/python3.4/urllib/request.py", line 481, in _open
 '_open', req)
 File "/usr/lib/python3.4/urllib/request.py", line 441, in _call_chain
 result = func(*args)
 File "/usr/lib/python3.4/urllib/request.py", line 1225, in https_open
 context=self._context, check_hostname=self._check_hostname)
 File "/usr/lib/python3.4/urllib/request.py", line 1184, in do_open
 raise URLError(err)
urllib.error.URLError: <urlopen error Tunnel connection failed: 407 Proxy Authentication Required>
Seems HTTP connection works while HTTPS not. I think it's a bug in urllib. For HTTPS connections, HTTPConnection.connect() calls HTTPConnection._tunnel(), and the latter function throws an OSError for 407 when sending a CONNECT request. There's no chance for OpenerDirector.open() to call HTTPErrorProcessor.http_response(). As a result, 407 errors are not handled correctly in ProxyDigestAuthHandler.http_error_407().
Finally, is there a workaround before this is fixed?

For those who are working on this problem, my squid.conf may be helpful:
--- squid.conf.default	2015年05月31日 03:33:34.006361795 +0800
+++ squid.conf	2015年05月31日 03:36:28.533034294 +0800
@@ -49,9 +49,15 @@
 # Example rule allowing access from your local networks.
 # Adapt localnet in the ACL section to list your (internal) IP networks
 # from where browsing should be allowed
-http_access allow localnet
-http_access allow localhost
+# http_access allow localnet
+# http_access allow localhost
 
+auth_param digest realm Proxy digest auth test
+auth_param digest program /usr/lib/squid/digest_file_auth -c /etc/squid/squid-passwd
+auth_param digest children 2
+
+acl squid-passwd proxy_auth REQUIRED
+http_access allow squid-passwd
 # And finally deny all other access to this proxy
 http_access deny all
And the content of /etc/squid/squid-passwd:
test_username:Proxy digest auth test:ab1e6b5de6ea6c8b072c5e513eea9c61
I'm testing for squid 3.5.5 on Arch Linux. I can test its correctness with curl:
$ curl -v --proxy-user test_username:test_password --proxy localhost:3128 --proxy-digest https://httpbin.org/ip 

There is already work done on this at Issue 7291. There is a patch there, but IMO it needs more work or a different approach.