MyHttpBrowser.py

import urllib2

class MyHttpBrowser(object):
    def __init__(self, baseUrl, loginUrl, username, password, digest = True):
        self.baseUrl = baseUrl
        self.loginUrl = loginUrl
        self.username = username
        self.password = password
        auth_handler = urllib2.HTTPDigestAuthHandler() if digest else urllib2.HTTPBasicAuthHandler()
        auth_handler.add_password(realm = 'Some Realm',
                                  uri = baseUrl,
                                  user = 'toto',
                                  passwd = '12345')
        proxy_handler = urllib2.ProxyHandler({})
        http_error_handler = MyHttpErrorHandler()

        self.opener = urllib2.build_opener(auth_handler, urllib2.HTTPCookieProcessor(),
                                           proxy_handler, http_error_handler)

MyHttpErrorHandler.py

import urllib2

class MyHttpErrorHandler(urllib2.HTTPDefaultErrorHandler):
    def http_error_default(self, req, fp, code, msg, hdrs):
        superMethod = urllib2.HTTPDefaultErrorHandler.http_error_default
        try:
            jsonResponse = json.load(fp)
            message = jsonResponse['errorMessage']
            if message:
                raise urllib2.HTTPError(req.get_full_url(), code, message, hdrs, fp)
            else:
                superMethod(self, req, fp, code, msg, hdrs)
        except json.JSONDecodeError:
            superMethod(self, req, fp, code, msg, hdrs)