A more explicit example, built on Damien's code (calls a test resource at http://httpbin.org/). For python3. Note that if the server redirects to another URL, uri in add_password has to contain the new root URL (it's possible to pass a list of URLs, also).
import ssl
import urllib.parse
import urllib.request
def get_resource(uri, user, passwd=False):
"""
Get the content of the SSL page.
"""
uri = 'https://httpbin.org/basic-auth/user/passwd'
user = 'user'
passwd = 'passwd'
context = ssl.create_default_context()
context.check_hostname = False
context.verify_mode = ssl.CERT_NONE
password_mgr = urllib.request.HTTPPasswordMgrWithDefaultRealm()
password_mgr.add_password(None, uri, user, passwd)
auth_handler = urllib.request.HTTPBasicAuthHandler(password_mgr)
opener = urllib.request.build_opener(auth_handler, urllib.request.HTTPSHandler(context=context))
urllib.request.install_opener(opener)
return urllib.request.urlopen(uri).read()