Name change required: hst:secured is confusing because it is like referring https.

From Ard's email:
"""
(Some people) separately from each other mentioned the confusing name
around 'secured' on mount and sitemapitem level. They stated,
correctly, that secured refers in general to https.

So, if we want to change it, we need to change it to something like
'authenticate' (when true, it means you need to be authenticated). Or,
we stick to the unfortunate name...
"""

And, from Ate's email:
"""
What about:

property: hst:secured -> hst:authenticated

• reason: authenticate could still also mean, "initiate authentication",
  while in this context I think it means "only allow access when authenticated"

method: isSecure() -> isAuthenticated()

• reason: same as above
  """