Cannot authenticate against Kerberized hgweb using Python 3

[Geert Lorang]

Hi list,

Trying to port 
https://bitbucket.org/domruf/hgssoauthentication/src/default/ to 
Merurial 5.3 with Python 3 but I'm running into following exception when 
either the extension is not loaded, no TGT or TGT expired:

$ hg pull
pulling from https://hidden/hg/testrepo/
** unknown exception encountered, please report by visiting
** https://mercurial-scm.org/wiki/BugTracker
** Python 3.7.5 (default, Nov 20 2019, 09:21:52) [GCC 9.2.1 20191008]
** Mercurial Distributed SCM (version 5.3)
** Extensions loaded: share, largefiles
...
ValueError: AbstractDigestAuthHandler does not support the following 
scheme: 'Negotiate'

When using Mercurial 5.3 with Python 2.7 there is no problem. After some 
investigating it seems Python 3.7's urllib will (now) unconditionally 
raise an exception when scheme is not digest or basic in 
AbstractDigestAuthHandler.

Python 2: /usr/lib/python2.7/urllib2.py:

class AbstractDigestAuthHandler:

 Â Â Â  def http_error_auth_reqed(self, authreq, host, req, headers):

 Â Â Â Â Â Â Â Â Â Â Â  if scheme.lower() == 'digest':
 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  return self.retry_http_digest_auth(req, authreq)

Python 3: /usr/lib/python3.7/urllib/request.py

class AbstractDigestAuthHandler:

 Â Â Â  def http_error_auth_reqed(self, authreq, host, req, headers):

 Â Â Â Â Â Â Â Â Â Â Â  if scheme.lower() == 'digest':
 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  return self.retry_http_digest_auth(req, authreq)
 Â Â Â Â Â Â Â Â Â Â Â  elif scheme.lower() != 'basic':
 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  raise ValueError("AbstractDigestAuthHandler does not 
support"
 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  " the following scheme: '%s'" % scheme)

Could I somehow override Mercurial from trying digest authentication 
(via the extension) and/or should Mercurial catch this exception and 
continue with other authentication mechanisms ?

Let me know if you need this as a bug in Bugzilla.

Thanks,
Geert