Pluggable Authentication

Based on zope.authentication, this package provides a flexible and pluggable authentication utility. Several common plugins are provided.


2.0.0a2 (unreleased)

  • Refactored zope.pluggableauth.plugins.session.redirectWithComeFrom into a reusable function.

2.0.0a1 (2013-02-21)

  • Added tox.ini and
  • Added support for Python 3.3.
  • Replaced deprecated zope.component.adapts usage with equivalent zope.component.adapter decorator.
  • Replaced deprecated zope.interface.implements usage with equivalent zope.interface.implementer decorator.
  • Dropped support for Python 2.4 and 2.5.

1.3 (2011-02-08)

1.2 (2010-12-16)

  • SessionCredentialsPlugin has a hook (_makeCredentials) that can be overriden in subclasses to store the credentials in the session differently.

    For example, you could use keas.kmi and encrypt the passwords of the currently logged-in users so they don't appear in plain text in the ZODB.

1.1 (2010-10-18)

  • Moved concrete IAuthenticatorPlugin implementations from to zope.pluggableauth.plugins.

    As a result projects that want to use the IAuthenticator plugins (previously found in do not automatically also pull in the* dependencies that are needed to register the ZMI views.

1.0.3 (2010-07-09)

  • Fixed dependency declaration.

1.0.2 (2010-07-90)

1.0.1 (2010-02-11)

  • Adapters are now declared in a new ZCML file : principalfactories.zcml. This avoids duplication errors in

1.0 (2010-02-05)

  • Splitting off from

Pluggable-Authentication Utility

The Pluggable-Authentication Utility (PAU) provides a framework for authenticating principals and associating information with them. It uses plugins and subscribers to get its work done.

For a pluggable-authentication utility to be used, it should be registered as a utility providing the zope.authentication.interfaces.IAuthentication interface.


The primary job of PAU is to authenticate principals. It uses two types of plug-ins in its work:

  • Credentials Plugins
  • Authenticator Plugins

Credentials plugins are responsible for extracting user credentials from a request. A credentials plugin may in some cases issue a 'challenge' to obtain credentials. For example, a 'session' credentials plugin reads credentials from a session (the "extraction"). If it cannot find credentials, it will redirect the user to a login form in order to provide them (the "challenge").

Authenticator plugins are responsible for authenticating the credentials extracted by a credentials plugin. They are also typically able to create principal objects for credentials they successfully authenticate.

Given a request object, the PAU returns a principal object, if it can. The PAU does this by first iterateing through its credentials plugins to obtain a set of credentials. If it gets credentials, it iterates through its authenticator plugins to authenticate them.

If an authenticator succeeds in authenticating a set of credentials, the PAU uses the authenticator to create a principal corresponding to the credentials. The authenticator notifies subscribers if an authenticated principal is created. Subscribers are responsible for adding data, especially groups, to the principal. Typically, if a subscriber adds data, it should also add corresponding interface declarations.

Simple Credentials Plugin

To illustrate, we'll create a simple credentials plugin:

>>> from zope import interface
>>> from zope.pluggableauth.authentication import interfaces
>>> @interface.implementer(interfaces.ICredentialsPlugin)
... class MyCredentialsPlugin(object):
...     def extractCredentials(self, request):
...         return request.get('credentials')
...     def challenge(self, request):
...         pass # challenge is a no-op for this plugin
...     def logout(self, request):
...         pass # logout is a no-op for this plugin

As a plugin, MyCredentialsPlugin needs to be registered as a named utility:

>>> myCredentialsPlugin = MyCredentialsPlugin()
>>> provideUtility(myCredentialsPlugin, name='My Credentials Plugin')

Simple Authenticator Plugin

Next we'll create a simple authenticator plugin. For our plugin, we'll need an implementation of IPrincipalInfo:

>>> @interface.implementer(interfaces.IPrincipalInfo)
... class PrincipalInfo(object):
...     def __init__(self, id, title, description):
... = id
...         self.title = title
...         self.description = description
...     def __repr__(self):
...         return 'PrincipalInfo(%r)' %

Our authenticator uses this type when it creates a principal info:

>>> @interface.implementer(interfaces.IAuthenticatorPlugin)
... class MyAuthenticatorPlugin(object):
...     def authenticateCredentials(self, credentials):
...         if credentials == 'secretcode':
...             return PrincipalInfo('bob', 'Bob', '')
...     def principalInfo(self, id):
...         pass # plugin not currently supporting search

As with the credentials plugin, the authenticator plugin must be registered as a named utility:

>>> myAuthenticatorPlugin = MyAuthenticatorPlugin()
>>> provideUtility(myAuthenticatorPlugin, name='My Authenticator Plugin')

Configuring a PAU

Finally, we'll create the PAU itself:

>>> from zope.pluggableauth import authentication
>>> pau = authentication.PluggableAuthentication('xyz_')

and configure it with the two plugins:

>>> pau.credentialsPlugins = ('My Credentials Plugin', )
>>> pau.authenticatorPlugins = ('My Authenticator Plugin', )

Using the PAU to Authenticate

>>> from zope.pluggableauth.factories import AuthenticatedPrincipalFactory
>>> provideAdapter(AuthenticatedPrincipalFactory)

We can now use the PAU to authenticate a sample request:

>>> from zope.publisher.browser import TestRequest
>>> print(pau.authenticate(TestRequest()))

In this case, we cannot authenticate an empty request. In the same way, we will not be able to authenticate a request with the wrong credentials:

>>> print(pau.authenticate(TestRequest(credentials='let me in!')))

However, if we provide the proper credentials:

>>> request = TestRequest(credentials='secretcode')
>>> principal = pau.authenticate(request)
>>> principal

we get an authenticated principal.

Multiple Authenticator Plugins

The PAU works with multiple authenticator plugins. It uses each plugin, in the order specified in the PAU's authenticatorPlugins attribute, to authenticate a set of credentials.

To illustrate, we'll create another authenticator:

>>> class MyAuthenticatorPlugin2(MyAuthenticatorPlugin):
...     def authenticateCredentials(self, credentials):
...         if credentials == 'secretcode':
...             return PrincipalInfo('black', 'Black Spy', '')
...         elif credentials == 'hiddenkey':
...             return PrincipalInfo('white', 'White Spy', '')
>>> provideUtility(MyAuthenticatorPlugin2(), name='My Authenticator Plugin 2')

If we put it before the original authenticator:

>>> pau.authenticatorPlugins = (
...     'My Authenticator Plugin 2',
...     'My Authenticator Plugin')

Then it will be given the first opportunity to authenticate a request:

>>> pau.authenticate(TestRequest(credentials='secretcode'))

If neither plugins can authenticate, pau returns None:

>>> print(pau.authenticate(TestRequest(credentials='let me in!!')))

When we change the order of the authenticator plugins:

>>> pau.authenticatorPlugins = (
...     'My Authenticator Plugin',
...     'My Authenticator Plugin 2')

we see that our original plugin is now acting first:

>>> pau.authenticate(TestRequest(credentials='secretcode'))

The second plugin, however, gets a chance to authenticate if first does not:

>>> pau.authenticate(TestRequest(credentials='hiddenkey'))

Multiple Credentials Plugins

As with with authenticators, we can specify multiple credentials plugins. To illustrate, we'll create a credentials plugin that extracts credentials from a request form:

>>> @interface.implementer(interfaces.ICredentialsPlugin)
... class FormCredentialsPlugin:
...     def extractCredentials(self, request):
...         return request.form.get('my_credentials')
...     def challenge(self, request):
...         pass
...     def logout(request):
...         pass
>>> provideUtility(FormCredentialsPlugin(),
...                name='Form Credentials Plugin')

and insert the new credentials plugin before the existing plugin:

>>> pau.credentialsPlugins = (
...     'Form Credentials Plugin',
...     'My Credentials Plugin')

The PAU will use each plugin in order to try and obtain credentials from a request:

>>> pau.authenticate(TestRequest(credentials='secretcode',
...                              form={'my_credentials': 'hiddenkey'}))

In this case, the first credentials plugin succeeded in getting credentials from the form and the second authenticator was able to authenticate the credentials. Specifically, the PAU went through these steps:

  • Get credentials using 'Form Credentials Plugin'
  • Got 'hiddenkey' credentials using 'Form Credentials Plugin', try to authenticate using 'My Authenticator Plugin'
  • Failed to authenticate 'hiddenkey' with 'My Authenticator Plugin', try 'My Authenticator Plugin 2'
  • Succeeded in authenticating with 'My Authenticator Plugin 2'

Let's try a different scenario:

>>> pau.authenticate(TestRequest(credentials='secretcode'))

In this case, the PAU went through these steps:

- Get credentials using 'Form Credentials Plugin'
  • Failed to get credentials using 'Form Credentials Plugin', try 'My Credentials Plugin'
  • Got 'scecretcode' credentials using 'My Credentials Plugin', try to authenticate using 'My Authenticator Plugin'
  • Succeeded in authenticating with 'My Authenticator Plugin'

Let's try a slightly more complex scenario:

>>> pau.authenticate(TestRequest(credentials='hiddenkey',
...                              form={'my_credentials': 'bogusvalue'}))

This highlights PAU's ability to use multiple plugins for authentication:

  • Get credentials using 'Form Credentials Plugin'
  • Got 'bogusvalue' credentials using 'Form Credentials Plugin', try to authenticate using 'My Authenticator Plugin'
  • Failed to authenticate 'boguskey' with 'My Authenticator Plugin', try 'My Authenticator Plugin 2'
  • Failed to authenticate 'boguskey' with 'My Authenticator Plugin 2' -- there are no more authenticators to try, so lets try the next credentials plugin for some new credentials
  • Get credentials using 'My Credentials Plugin'
  • Got 'hiddenkey' credentials using 'My Credentials Plugin', try to authenticate using 'My Authenticator Plugin'
  • Failed to authenticate 'hiddenkey' using 'My Authenticator Plugin', try 'My Authenticator Plugin 2'
  • Succeeded in authenticating with 'My Authenticator Plugin 2' (shouts and cheers!)

Multiple Authenticator Plugins

As with the other operations we've seen, the PAU uses multiple plugins to find a principal. If the first authenticator plugin can't find the requested principal, the next plugin is used, and so on.

>>> @interface.implementer(interfaces.IAuthenticatorPlugin)
... class AnotherAuthenticatorPlugin:
...     def __init__(self):
...         self.infos = {}
...         self.ids = {}
...     def principalInfo(self, id):
...         return self.infos.get(id)
...     def authenticateCredentials(self, credentials):
...         id = self.ids.get(credentials)
...         if id is not None:
...             return self.infos[id]
...     def add(self, id, title, description, credentials):
...         self.infos[id] = PrincipalInfo(id, title, description)
...         self.ids[credentials] = id

To illustrate, we'll create and register two authenticators:

>>> authenticator1 = AnotherAuthenticatorPlugin()
>>> provideUtility(authenticator1, name='Authentication Plugin 1')
>>> authenticator2 = AnotherAuthenticatorPlugin()
>>> provideUtility(authenticator2, name='Authentication Plugin 2')

and add a principal to them:

>>> authenticator1.add('bob', 'Bob', 'A nice guy', 'b0b')
>>> authenticator1.add('white', 'White Spy', 'Sneaky', 'deathtoblack')
>>> authenticator2.add('black', 'Black Spy', 'Also sneaky', 'deathtowhite')

When we configure the PAU to use both searchable authenticators (note the order):

>>> pau.authenticatorPlugins = (
...     'Authentication Plugin 2',
...     'Authentication Plugin 1')

we register the factories for our principals:

>>> from zope.pluggableauth.factories import FoundPrincipalFactory
>>> provideAdapter(FoundPrincipalFactory)

we see how the PAU uses both plugins:

>>> pau.getPrincipal('xyz_white')
>>> pau.getPrincipal('xyz_black')

If more than one plugin know about the same principal ID, the first plugin is used and the remaining are not delegated to. To illustrate, we'll add another principal with the same ID as an existing principal:

>>> authenticator2.add('white', 'White Rider', '', 'r1der')
>>> pau.getPrincipal('xyz_white').title
'White Rider'

If we change the order of the plugins:

>>> pau.authenticatorPlugins = (
...     'Authentication Plugin 1',
...     'Authentication Plugin 2')

we get a different principal for ID 'white':

>>> pau.getPrincipal('xyz_white').title
'White Spy'

Issuing a Challenge

Part of PAU's IAuthentication contract is to challenge the user for credentials when its 'unauthorized' method is called. The need for this functionality is driven by the following use case:

  • A user attempts to perform an operation he is not authorized to perform.
  • A handler responds to the unauthorized error by calling IAuthentication 'unauthorized'.
  • The authentication component (in our case, a PAU) issues a challenge to the user to collect new credentials (typically in the form of logging in as a new user).

The PAU handles the credentials challenge by delegating to its credentials plugins.

Currently, the PAU is configured with the credentials plugins that don't perform any action when asked to challenge (see above the 'challenge' methods).

To illustrate challenges, we'll subclass an existing credentials plugin and do something in its 'challenge':

>>> class LoginFormCredentialsPlugin(FormCredentialsPlugin):
...     def __init__(self, loginForm):
...         self.loginForm = loginForm
...     def challenge(self, request):
...         request.response.redirect(self.loginForm)
...         return True

This plugin handles a challenge by redirecting the response to a login form. It returns True to signal to the PAU that it handled the challenge.

We will now create and register a couple of these plugins:

>>> provideUtility(LoginFormCredentialsPlugin('simplelogin.html'),
...                name='Simple Login Form Plugin')
>>> provideUtility(LoginFormCredentialsPlugin('advancedlogin.html'),
...                name='Advanced Login Form Plugin')

and configure the PAU to use them:

>>> pau.credentialsPlugins = (
...     'Simple Login Form Plugin',
...     'Advanced Login Form Plugin')

Now when we call 'unauthorized' on the PAU:

>>> request = TestRequest()
>>> pau.unauthorized(id=None, request=request)

we see that the user is redirected to the simple login form:

>>> request.response.getStatus()
>>> request.response.getHeader('location')

We can change the challenge policy by reordering the plugins:

>>> pau.credentialsPlugins = (
...     'Advanced Login Form Plugin',
...     'Simple Login Form Plugin')

Now when we call 'unauthorized':

>>> request = TestRequest()
>>> pau.unauthorized(id=None, request=request)

the advanced plugin is used because it's first:

>>> request.response.getStatus()
>>> request.response.getHeader('location')

Challenge Protocols

Sometimes, we want multiple challengers to work together. For example, the HTTP specification allows multiple challenges to be issued in a response. A challenge plugin can provide a challengeProtocol attribute that effectively groups related plugins together for challenging. If a plugin returns True from its challenge and provides a non-None challengeProtocol, subsequent plugins in the credentialsPlugins list that have the same challenge protocol will also be used to challenge.

Without a challengeProtocol, only the first plugin to succeed in a challenge will be used.

Let's look at an example. We'll define a new plugin that specifies an 'X-Challenge' protocol:

>>> class XChallengeCredentialsPlugin(FormCredentialsPlugin):
...     challengeProtocol = 'X-Challenge'
...     def __init__(self, challengeValue):
...         self.challengeValue = challengeValue
...     def challenge(self, request):
...         value = self.challengeValue
...         existing = request.response.getHeader('X-Challenge', '')
...         if existing:
...             value += ' ' + existing
...         request.response.setHeader('X-Challenge', value)
...         return True

and register a couple instances as utilities:

>>> provideUtility(XChallengeCredentialsPlugin('basic'),
...                name='Basic X-Challenge Plugin')
>>> provideUtility(XChallengeCredentialsPlugin('advanced'),
...                name='Advanced X-Challenge Plugin')

When we use both plugins with the PAU:

>>> pau.credentialsPlugins = (
...     'Basic X-Challenge Plugin',
...     'Advanced X-Challenge Plugin')

and call 'unauthorized':

>>> request = TestRequest()
>>> pau.unauthorized(None, request)

we see that both plugins participate in the challange, rather than just the first plugin:

>>> request.response.getHeader('X-Challenge')
'advanced basic'

Pluggable-Authentication Prefixes

Principal ids are required to be unique system wide. Plugins will often provide options for providing id prefixes, so that different sets of plugins provide unique ids within a PAU. If there are multiple pluggable-authentication utilities in a system, it's a good idea to give each PAU a unique prefix, so that principal ids from different PAUs don't conflict. We can provide a prefix when a PAU is created:

>>> pau = authentication.PluggableAuthentication('mypau_')
>>> pau.credentialsPlugins = ('My Credentials Plugin', )
>>> pau.authenticatorPlugins = ('My Authenticator Plugin', )

When we create a request and try to authenticate:

>>> pau.authenticate(TestRequest(credentials='secretcode'))

Note that now, our principal's id has the pluggable-authentication utility prefix.

We can still lookup a principal, as long as we supply the prefix:

>> pau.getPrincipal('mypas_42')
Principal('mypas_42', "{'domain': 42}")

>> pau.getPrincipal('mypas_41')
OddPrincipal('mypas_41', "{'int': 41}")