It looks like some servers using basic authentication don't include quotes around the realm (example https://api.connect2field.com) as required by rfc 2617. urllib wont handle these requests and silently fails, but a simple change to the regex in AbstractBasicAuthHandler from
 
'realm=(["\'])(.*?)\\2', re.I)
to
'realm=(["\']?)(["\']*)\\2', re.I)

would make authentication more flexible.

For some reason a caret went missing in the regex fix.
It should read

'realm=(["\']?)([^"\']*)\\2', re.I)

Here is a patch with the test for accepting the badly formed headers. I would like to ensure that change in the regex is fool-proof in order to accomodate this bad behavior, so that we don't break the existing stuff.

It is problem at the server end,I found that browsers thrown warning before accepting that.

Perhaps we should issue a warning, then, too?

I don't think so. We are just making our regex bit lenient. I am not
sure how we can raise a warning with more lenient regex.

As with any parsing changes, I would like to be careful and that we
don't introduce any regression.

It could have a 2 phase regex match. We match the first one, and if it fails, match the second and produce a warning. 

I think producing a warning is a good idea, as it allows the programmer to know that the implementation of basic auth they are trying to connect to is broken, and might help with future connection attempts. Also there are currently no warnings produced by python if it fails to parse the auth header, and its hard for a developer to know why.

I think a warning would be quite nice to have.

New changeset 3e10d0148f79 by Senthil Kumaran in branch '2.7':
Issue #12541: Be lenient with quotes around Realm field with HTTP Basic Authentation in urllib2.
http://hg.python.org/cpython/rev/3e10d0148f79

New changeset bb94fec5c5ab by Senthil Kumaran in branch '3.2':
Issue #12541: Be lenient with quotes around Realm field of HTTP Basic Authentation in urllib2.
http://hg.python.org/cpython/rev/bb94fec5c5ab

New changeset bf20564296aa by Senthil Kumaran in branch 'default':
merge from 3.2 - Issue #12541: Be lenient with quotes around Realm field of HTTP Basic Authentation in urllib2.
http://hg.python.org/cpython/rev/bf20564296aa

New changeset b82178b07e0f by Senthil Kumaran in branch '2.7':
Issue12541 - Add UserWarning for unquoted realms
http://hg.python.org/cpython/rev/b82178b07e0f

New changeset b5b38bda9fc4 by Senthil Kumaran in branch '3.2':
Issue12541 - Add UserWarning for unquoted realms
http://hg.python.org/cpython/rev/b5b38bda9fc4

New changeset 08fa1a47fa97 by Senthil Kumaran in branch 'default':
Issue12541 - Add UserWarning for unquoted realms
http://hg.python.org/cpython/rev/08fa1a47fa97

this issue is taken care. Both in accepting unquoted Realm for basic auth leniently and then raising a UserWarning when encountering this case.