An anonymous user who tries to access the bugtask edit page will be
redirected to the login page.

    >>> browser.open("http://launchpad.dev/thunderbird/+bug/9/+editstatus")
    Traceback (most recent call last):
      ...
    Unauthorized: ...

Even when the product has a bug supervisor, see bug #49891.

    >>> from zope.component import getUtility
    >>> from lp.services.database.sqlbase import flush_database_updates
    >>> from lp.testing import login, logout
    >>> from lp.registry.interfaces.person import IPersonSet
    >>> from lp.registry.interfaces.product import IProductSet

    >>> login("test@canonical.com")

    >>> from lp.services.database.lpstorm import IMasterObject
    >>> firefox = IMasterObject(getUtility(IProductSet).getByName("firefox"))
    >>> sample_person = IMasterObject(
    ...     getUtility(IPersonSet).getByName("name12"))
    >>> firefox.setBugSupervisor(sample_person, sample_person)

    >>> flush_database_updates()

    >>> logout()

    >>> browser.open("http://launchpad.dev/firefox/+bug/1/+editstatus")
    Traceback (most recent call last):
      ...
    Unauthorized: ...

Any logged-in user can edit a bugtask.

    >>> browser = setupBrowser(auth="Basic test@canonical.com:test")
    >>> browser.open("http://launchpad.dev/firefox/+bug/6/+editstatus")
    >>> print browser.title
    Edit status ...