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Merge pull request #3 from plone/tomgross-ptc

Removed unused egg dependency
latest commit ea785c02b4
Timo Stollenwerk tisto authored
README.txt
Overview
========

plone.session implements secure session management for Zope sites.

In its default configuration plone.session uses an HMAC_ SHA-256_ secure
cryptographic hash to authenticate sessions. The hash is generated using the
userid and a secret stored in the PAS plugin. Otherwise, the cookie
format is identical to that of Apache's mod_auth_tkt_. For single sign on with
the original mod_auth_tkt or another compatible implementation, set the
``mod_auth_tkt`` property to true. This invokes an MD5_ based double hashing
scheme. You will need to use the same secret across all servers.

This has several advantages over other session management systems:

* passwords are not sent to the server in a cookie on every request, as
  is done by the *Cookie Auth Helper* 
* it does not require any ZODB write for sessions, as is needed by the
  *Session Crumbler*. This allows it to scale very well.
* it allows you to invalidate all existing authentication cookies for
  users by updating the secret.
* The cookie is only valid for the period specified by the `timeout` property.

There are some downsides to this approach:

* if a user's password is changed or disabled session identifiers will
  continue to work, making it hard to lock out individual users.
* a user must have cookies enabled.

A session cookie is used to track sessions; that means that as long as
a user keeps his browser open (and does not explicitly log out) the session
remains open until the timout limit is reached. This can be changed by setting
the ``timeout`` property of the plugin to the number of seconds the cookie
should remain valid *after the moment of login*. 

`tktauth.py` implements the core mod_auth_tkt functionality. It is
self-contained and may be of useful to other frameworks.

.. _mod_auth_tkt: http://www.openfusion.com.au/labs/mod_auth_tkt/
.. _MD5: http://en.wikipedia.org/wiki/MD5
.. _HMAC: http://en.wikipedia.org/wiki/HMAC
.. _SHA-256: http://en.wikipedia.org/wiki/SHA-256


Using plone.session
===================

plone.session only takes care of handling sessions for already authenticated
users. This means it can not be used stand-alone: you need to have another
PAS plugin, such as the standard *Cookie Auth Helper* to take care of
authentication.

After a user has been authenticated plone.session can take over via the
PAS *credentials update* mechanism. 

Python 2.4 / Zope 2.10 / Plone 3
--------------------------------

To use this version of plone.session under Python 2.4, add the `backported
hmac`_ module to your buildout (which will also bring in the backported
hashlib_ module.)

.. _`backported hmac`: http://pypi.python.org/pypi/hmac
.. _hashlib: http://pypi.python.org/pypi/hashlib


Configuration options
=====================

To enable logins between sites or other mod_auth_tkt systems, set the shared
secret through the Zope Management Interface. You can manage the plone.keyring
secrets through the same page.

The following properties may be set through the Properties tab:

  Cookie validity timeout (in seconds)
    After this, the session is invalid and the user must login again. Set to 0
    for the cookie to remain valid indefinitely. Note that when the user
    folder has caching enabled, cookie validity may not be checked on every
    request.

  Refresh interval (in seconds, -1 to disable refresh)
    This controls the refresh CSS max-age (see below.)

  Use mod_auth_tkt compatible hashing algorithm
    Compatibility with other implemenations, but at the cost of using a weaker
    hashing algorithm.

  Cookie name
    Which cookie to use. This must also be set on the
    ``credentials_cookie_auth`` plugin.

  Cookie lifetime (in days)
    This makes the cookie persistent across opening and closing the browser.

  Cookie domain (blank for default)
    A cookie may be shared across www1.example.com and www2.example.com by
    setting the cookie domain to ``.example.com``.

  Cookie path
    What path the cookie is set valid (defaults to ``/``.)


Ticket refresh
==============

To enable short validity timeouts you must ensure that the cookie is regularly
updated. One option is to put mod_auth_tkt in front of your site and set a
``TktAuthTimeoutRefresh``. As of plone.session 3.1, an independent javascript
solution is also supplied, installable as an optional add-on in Plone.

Theory of operation
-------------------

The optional add-on installs a css resource which updates the cookie when
loaded. This allows the cookie to be updated every time a page is loaded.
While this CSS cannot cached by proxy servers, it may be cached for a time on
the client. By controlling the ``max-age`` of the CSS resource, it is possible
to control how often the browser actually fetches the CSS and hence how often
the cookie is updated.

With short timeouts (15 or 30 minutes say), a user may not have loaded a new
page before their cookie becomes invalid. A javascript is included which polls
the cookie refresh CSS periodically while the user is active on the page (key
presses or mouse moves.) If the refresh CSS max-age has passed, then the
browser will refetch the CSS and the cookie will be updated. The poll interval
may be configured on the refresh CSS query string ``minutes`` parameter, with
the default being 5 minutes.

Caveat
------

This has been tested and shown to work on Internet Explorer 7, Firefox 4,
Safari 5 and Chrome 6. Unfortunately Internet Explorer 6 does not seem to
respect the caching headers for javascript fetched resources, so if you have a
lot of IE6 users you may want to increase the poll interval to reduce server
load.


Ticket removal
==============

When login sessions are shared across domains, it can be helpful to log users
out of all domains when they log out of a Plone site. This may be configured
in `portal_css` by adding a resource with the following settings

  ID/URL
    ``http://example.com/portal_path/acl_users/session/remove?type=css``
    (adjusted to the url of the portal to be logged out.)

  Condition
    ``python:request.URL.endswith('/logged_out')``

  Render type
    link

  Compression type
    none

  Merging allowed?
    No

  Caching allowed?
    No

  CSS Media
    (blank)

Single Sign On with IIS
=======================

For intranet setups with users on a Windows domain, it's possible to configure IIS with `Integrated Windows Authentication` to act as an external login provider, even for sites running on Linux/Unix servers.


Requirements
------------

- You need a Microsoft Windows Server running IIS. Preferably Windows Server
  2003 or a later version.

- The server must be a member of the Windows domain you want to authenticate
  users for. It does not need to be an Active Directory server itself.

- You site should use LDAPMultiPlugins_ to use the same Active Directory as a
  user source. (Use plone.app.ldap_ to set this up with Plone.)

.. _LDAPMultiPlugins: http://pypi.python.org/pypi/Products.LDAPMultiPlugins
.. _plone.app.ldap: http://pypi.python.org/pypi/plone.app.ldap


Python
------

- The Windows server needs to have `Python 2.6
  <http://www.python.org/download/>` and the `Python Win 32 extensions
  <http://sourceforge.net/projects/pywin32/files/>`_ installed. (Currently
  Python 2.6.5 and pywin32-214.)

- Until pywin32-215 is released, apply this `fix
  <http://mail.python.org/pipermail/python-win32/2009-October/009639.html>`_
  to the file::

    C:\Python26\Lib\site-packages\win32comext\axscript\client\framework.py

  and remove the framework.pyc and framework.pyo files.

- Place a copy of ``tktauth.py`` (from plone/session of this package) into::

    C:\Python26\Lib\site-packages\

- Follow these `instructions on how to configure Python for IIS
  <http://support.microsoft.com/kb/276494>`_. In bullet point 2.d. use::

    Executable: "C:\Python26\python.exe -u %s %s"

  instead. This will ensure files are opened in universal newline mode. You
  can choose to only configure these settings for the specific web site and
  not the entire IIS. Adjust settings accordingly and create the web site
  first as detailed in the next chapter.


IIS
---

- Find and open the IIS management console.

- Create a new `Web Site`, by going into the `Web Sites` folder and using the
  right-click menu. You should get a wizard asking you for various questions::

    Description: SSO login service

    TCP port: 80

    Path: c:\Inetpub\sso

    Allow anonymous access to this Web site: <not checked>

    Permissions: Read, Run scripts, Execute

- If you are running IIS 6, you need to go to the `Web Service Extensions`
  folder and change `Active Server Pages` to be `Allowed`. Otherwise you
  will get rather unhelpful `404 Not Found` errors for the asp scripts.


IIS script
----------

- Copy the `login.asp` and `test.asp` scripts (from the iis-login folder of
  this package) into root path of the web site (for example C:\Inetpub\sso).

- You need to modify the `SECRET` constant found in the `login.asp` to the
  same shared secret set on plone.session's `Manage secrets` tab.

- Modify the `ALLOWED_SITES` constant in `login.asp` to include the URLs of
  your Plone sites.

- Modify the `DEFAULT_NEXT` constant in `login.asp` to refer the the URL of
  `logged_in` on one of your Plone sites.

- Access http://LOGONSERVER/test.asp to confirm access permissions are
  correctly configured.


Configuring browsers to allow automatic logon
---------------------------------------------

Browsers must be configured to "trust" the logon server for user
authentication data to be sent automatically.

By default, Internet Explorer sends logon information to servers within the
"Intranet Zone", so long as the site is accessed using it's intranet name
(http://LOGONSERVER/login.asp). If the site is accessed using a fully
qualified domain name or IP address, it must be explicitly added to the list
of `trusted sites <http://support.microsoft.com/kb/174360>`_.

Firefox configuration information may be found in this `article
<http://support.mozilla.com/en-US/kb/Firefox+asks+for+user+name+and+password+on+internal+sites>`_.


Configuring your Plone site
---------------------------

Ensure that you have setup authentication to Active Directory and that you can
login with the your current Windows user name.

Set the following configuration options through the Zope interface:

- In `/Plone/acl_users/session`. On the `Manage secrets` tab set a shared
  secret.

- In `/Plone/portal_properties/site_properties` set `external_login_url` to
  `http://LOGONSERVER/login.asp`.

For Plone versions before 4.1:

- In `/Plone/portal_actions/user/login`. On the `Properties` tab set `URL
  (Expression)` to `${portal/portal_properties/site_properties/external_login_url}?next=${globals_view/navigationRootUrl}/logged_in`.

For Plone 4.1 and later you may instead set:

- In `/Plone/portal_properties/site_properties` set `external_login_iframe` to
  True.

Note for developers testing this under Windows XP
-------------------------------------------------

- IIS may be installed as an additional component using the Windows XP
  installation CD.

- The IIS management console can be located at::

    Start -> Control Panel -> Adminstrative Tools -> Internet Information Services

- The pywin32 installer setup IIS sufficiently for me not to need to follow
  the `instructions on how to configure Python for IIS`.

- I could not find how to setup a separate site, so placed the asp scripts
  directly in C:\Inetpub\wwwroot - the "Default Web Site"

- From the IIS management console, select "Default Web Site". You should see
  `login.asp` and `test.asp` in the right hand pane. With each file,
  right-click Properties. On the `File Security` tab click Edit... on
  `Anonymous access and authentication control`. Uncheck `Anonymous access`
  and check `Basic authentication` (to be used as a fallback) and `Integrated
  Windows authentication`.

- Access http://localhost/test.asp to confirm IIS authentication works as
  expected.

- Set the secret in `login.asp` and `Manage secrets` of plone.session.

- Set SITE_URL in `login.asp` to `http://localhost:8080/Plone` (or whatever
  the address of your site is.)

- Add a Plone user with the same name as your Windows login name (e.g.
  Administrator), this avoids setting up Active Directory.

- Follow the section above to configure your Plone site, but set `Login Form`
  to `http://localhost/login.asp`.
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