Depending on your server (Unix or Windows) you might have a 'control panel'
with a feature to set 'protected folders' up on your site. You can add
users/passwords to a list and when the person browsers to the protected
folder/page they will get a dialogue box prompting them for the username and
password to access that page. It would be very simple but effective
protection - to log out the user would just close the browser window. To
revisit the page, they just browse/click a link to it and again the prompt
will come up.
If you have "HELM" control panel on a windows server or "cPanel" on Linux,
these should have this feature, but it would depend on your host as well, so
it would be best to ask them.
Having said that, I don't know what effect the above will have on the server
extensions if they're enabled, in terms of corrupting them or disabling them
unexpectedly etc. Again, check with your host.