***************************************************
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:mod:`repoze.who` -- WSGI Authentication Middleware
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***************************************************
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:Author: Chris McDonough
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:Version: |version|
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.. module:: repoze.who
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:synopsis: WSGI authentication middleware
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.. topic:: Overview
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``repoze.who`` is an identification and authentication framework
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for arbitrary WSGI applications. It acts as WSGI middleware.
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``repoze.who`` is inspired by Zope 2's Pluggable Authentication
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Service (PAS) (but ``repoze.who`` is not dependent on Zope in any
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way; it is useful for any WSGI application). It provides no
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facility for authorization (ensuring whether a user can or cannot
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perform the operation implied by the request). This is considered
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to be the domain of the WSGI application.
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It attemtps to reuse implementations from ``paste.auth`` for some
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of its functionality.
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Middleware Responsibilities
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===========================
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``repoze.who`` as middleware has one major function on ingress: it
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conditionally places identification and authentication information
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(including a ``REMOTE_USER`` value) into the WSGI environment and
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allows the request to continue to a downstream WSGI application.
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``repoze.who`` as middleware has one major function on egress: it
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examines the headers set by the downstream application, the WSGI
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environment, or headers supplied by other plugins and conditionally
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challenges for credentials.
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Configuration Points
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====================
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Classifiers
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-----------
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``repoze.who`` "classifies" the request on middleware ingress.
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Request classification happens before identification and
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authentication. A request from a browser might be classified a
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different way that a request from an XML-RPC client. ``repoze.who``
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uses request classifiers to decide which other components to consult
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during subsequent identification, authentication, and challenge steps.
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Plugins are free to advertise themselves as willing to participate in
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identification and authorization for a request based on this
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classification. The request classification system is pluggable.
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``repoze.who`` provides a default classifier that you may use. You
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may extend the classification system by making ``repoze.who`` aware of
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a different request classifier implementation.
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Challenge Deciders
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------------------
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``repoze.who`` uses a "challenge decider" to decide whether the
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response returned from a downstream application requires a challenge
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plugin to fire. When using the default challenge decider, only the
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status is used (if it starts with ``401``, a challenge is required).
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You may supply a different challenge decider as necessary.
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Plugins
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-------
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``repoze.who`` has core functionality designed around the concept of
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plugins. Plugins are instances that are willing to perform one or
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more identification- and/or authentication-related duties. Each
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plugin can be configured arbitrarily.
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``repoze.who`` consults the set of configured plugins when it
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intercepts a WSGI request, and gives some subset of them a chance to
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influence what ``repoze.who`` does for the current request.
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Lifecycle of a Request
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======================
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``repoze.who`` performs duties both on middleware "ingress" and on
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middleware "egress".
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Request (Ingress) Stages
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------------------------
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``repoze.who`` performs the following operations in the following order
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during middleware ingress:
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1. Request Classification
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The WSGI environment is examined and the request is classified
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into one "type" of request. The callable named as the
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``classifer`` argument to the ``repoze.who`` middleware
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constructor is used to perform the classification. It returns a
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value that is considered to be the request classification (a
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single string).
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2. Identification
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Identifiers which nominate themselves as willing to extract data
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for a particular class of request (as provided by the request
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classifier) will be consulted to retrieve credentials data from
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the environment. For example, a basic auth identifier might use
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the ``HTTP_AUTHORIZATION`` header to find login and password
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information. Identifiers are also responsible for providing
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header information to set and remove authentication information in
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the response during egress.
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3. Authentication
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Authenticators which nominate themselves as willing to
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authenticate for a particular class of request will be consulted
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to compare information provided by the identification plugins
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that returned credentials. For example, an htpasswd
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authenticator might look in a file for a user record matching
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any of the identities. If it finds one, and if the password
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listed in the record matches the password provided by an
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identity, the userid of the user would be returned (which would
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be the same as the login name).
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4. Metadata Provision
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The identity of the authenticated user found during the
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authentication step can be augmented with arbitrary metadata.
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For example, a metadata provider plugin might augment the
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identity with first, middle and last names, or a more
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specialized metadata provider might augment the identity with a
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list of role or group names.
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Response (Egress) Stages
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------------------------
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``repoze.who`` performs the following operations in the following order
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during middleware egress:
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1. Challenge Decision
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The WSGI environment and the status and headers returned by the
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downstream application may be examined to determine whether a
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challenge is required. Typically, only the status is used (if it
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starts with ``401``, a challenge is required, and the challenge
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decider returns True). This behavior is pluggable. It is
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replaced by changing the ``challenge_decider`` argument to the
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middleware. If a challenge is required, the challenge decider
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will return True; if it's not, it will return False.
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2. Challenge
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If the challenge decider returns True, challengers which nominate
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themselves as willing to execute a challenge for a particular
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class of request (as provided by the classifier) will be
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consulted, and one will be chosen to perform a challenge. A
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challenger plugin can use application-returned headers, the WSGI
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environment, and other items to determine what sort of operation
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should be performed to actuate the challenge. Note that
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``repoze.who`` defers to the identifier plugin which provided the
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identity (if any) to reset credentials at challenge time; this is
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not the responsibility of the challenger. This is known as
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"forgetting" credentials.
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3. Remember
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The identifier plugin that the "best" set of credentials came from
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(if any) will be consulted to "remember" these credentials if the
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challenge decider returns False.
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Plugin Types
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============
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Identifier Plugins
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------------------
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You can register a plugin as willing to act as an "identifier". An
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identifier examines the WSGI environment and attempts to extract
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credentials from the environment. These credentials are used by
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authenticator plugins to perform authentication. In some cases, an
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identification plugin can "preauthenticate" an identity (and can thus
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act as an authenticator plugin).
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Authenticator Plugins
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---------------------
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You may register a plugin as willing to act as an "authenticator".
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Authenticator plugins are responsible for resolving a set of
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credentials provided by an identifier plugin into a user id.
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Typically, authenticator plugins will perform a lookup into a database
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or some other persistent store, check the provided credentials against
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the stored data, and return a user id if the credentials can be
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validated.
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The user id provided by an authenticator is eventually passed to
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downstream WSGI applications in the "REMOTE_USER' environment
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variable. Additionally, the "identity" of the user (as provided by
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the identifier from whence the identity came) is passed along to
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downstream application in the ``repoze.who.identity`` environment
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variable.
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Metadata Provider Plugins
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-------------------------
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You may register a plugin as willing to act as a "metadata provider"
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(aka mdprovider). Metadata provider plugins are responsible for
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adding arbitrary information to the identity dictionary for
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consumption by downstream applications. For instance, a metadata
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provider plugin may add "group" information to the the identity.
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Challenger Plugins
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------------------
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You may register a plugin as willing to act as a "challenger".
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Challenger plugins are responsible for initiating a challenge to the
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requesting user. Challenger plugins are invoked by ``repoze.who`` when it
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decides a challenge is necessary. A challenge might consist of
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displaying a form or presenting the user with a basic or digest
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authentication dialog.
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Default Plugin Implementations
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==============================
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``repoze.who`` ships with a variety of default plugins that do
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authentication, identification, challenge and metadata provision.
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.. module:: repoze.who.plugins.auth_tkt
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.. class:: AuthTktCookiePlugin(secret [, cookie_name='auth_tkt' [, secure=False [, include_ip=False]]])
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An :class:`AuthTktCookiePlugin` is an ``IIdentifier`` plugin which
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remembers its identity state in a client-side cookie. This plugin
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uses the ``paste.auth.auth_tkt``"auth ticket" protocol. It should
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be instantiated passing a *secret*, which is used to encrypt the
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cookie on the client side and decrypt the cookie on the server side.
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The cookie name used to store the cookie value can be specified
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using the *cookie_name* parameter. If *secure* is False, the cookie
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will be sent across any HTTP or HTTPS connection; if it is True, the
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cookie will be sent only across an HTTPS connection. If
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*include_ip* is True, the ``REMOTE_ADDR`` of the WSGI environment
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will be placed in the cookie.
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.. module:: repoze.who.plugins.basicauth
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.. class:: BasicAuthPlugin(realm)
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A :class:`BasicAuthPlugin` plugin is both an ``IIdentifier`` and
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``IChallenger`` plugin that implements the Basic Access
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Authentication scheme described in :rfc:`2617`. It looks for
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credentials within the ``HTTP-Authorization`` header sent by
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browsers. It challenges by sending an ``WWW-Authenticate`` header
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to the browser. The single argument *realm* indicates the basic
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auth realm that should be sent in the ``WWW-Authenticate`` header.
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.. module:: repoze.who.plugins.cookie
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.. class:: InsecureCookiePlugin(cookie_name)
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A :class:`InsecureCookiePlugin` is an ``IIdentifier`` plugin. It
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stores identification information in an insecure form (the base64
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value of the username and password separated by a colon) in a
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client-side cookie. It accepts a single argument named
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*cookie_name*. This is the cookie name of the cookie used to store
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the identification information.
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.. module:: repoze.who.plugins.form
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.. class:: FormPlugin(login_form_qs, rememberer_name [, formbody=None [, formcallable=None]])
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A :class:`FormPlugin` is both an ``IIdentifier`` and ``IChallenger``
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plugin. It intercepts form POSTs to gather identification at
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ingress and conditionally displays a login form at egress if
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challenge is required. *login_form_qs* is a query string name used
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to denote that a form POST is destined for the form plugin (anything
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unique is fine), *rememberer_name* is the "configuration name" of
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another ``IIdentifier`` plugin that will be used to perform
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``remember`` and ``forget`` duties for the FormPlugin (it does not
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do these itself). For example, if you have a cookie identification
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plugin named ``cookie`` defined in your middleware configuration,
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you might set *rememberer_name* to ``cookie``. *formbody* is a
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literal string that should be displayed as the form body.
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*formcallable* is a callable that will return a form body if
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*formbody* is None. If both *formbody* and *formcallable* are None,
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a default form is used.
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.. class:: RedirectingFormPlugin(login_form_url, login_handler_path, logout_handler_path, rememberer_name)
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A :class:`RedirectingFormPlugin` is both an ``IIdentifier`` and
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``IChallenger`` plugin. It intercepts form POSTs to gather
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identification at ingress and conditionally redirects a login form
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at egress if challenge is required (as opposed to the
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:class:`FormPlugin`, it does not handle its own form generation).
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*login_form_url* is a URL that should be redirected to when a
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challnge is required. *login_handler_path* is the path that the
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form will POST to, signifying that the plugin should gather
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credentials. *logout_handler_path* is a path that can be called to
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log the current user out when visited. *rememberer_name* is the
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configuration name of another ``IIdentifier`` plugin that will be
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used to perform ``remember`` and ``forget`` duties for the
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RedirectingFormPlugin (it does not do these itself). For example,
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if you have a cookie identification plugin named ``cookie`` defined
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in your middleware configuration, you might set *rememberer_name* to
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``cookie``.
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.. module:: repoze.who.plugins.htpasswd
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.. class:: HTPasswdPlugin(filename, check)
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A :class:`HTPasswdPlugin` is an ``IAuthenticator`` implementation
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which compares identity information against an Apache-style htpasswd
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file. The *filename* argument should be an absolute path to the
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htpasswd file' the *check* argument is a callable which takes two
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arguments: "password" and "hashed", where the "password" argument is
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the unencrypted password provided by the identifier plugin, and the
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hashed value is the value stored in the htpasswd file. If the
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hashed value of the password matches the hash, this callable should
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return True. A default implementation named ``crypt_check`` is
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available for use as a check function (on UNIX) as
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``repoze.who.plugins.htpasswd:crypt_check``; it assumes the values
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in the htpasswd file are encrypted with the UNIX ``crypt`` function.
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.. module:: repoze.who.plugins.sql
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.. class:: SQLAuthenticatorPlugin(query, conn_factory, compare_fn)
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A :class:`SQLAuthenticatorPlugin` is an ``IAuthenticator``
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implementation which compares login-password identity information
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against data in an arbitrary SQL database. The *query* argument
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should be a SQL query that returns two columns in a single row
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considered to be the user id and the password respectively. The SQL
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query should contain Python-DBAPI style substitution values for
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``%(login)``, e.g. ``SELECT user_id, password FROM users WHERE login
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= %(login)``. The *conn_factory* argument should be a callable that
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returns a DBAPI database connection. The *compare_fn* argument
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should be a callable that accepts two arguments: ``cleartext`` and
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``stored_password_hash``. It should compare the hashed version of
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cleartext and return True if it matches the stored password hash,
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otherwise it should return False. A comparison function named
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``default_password_compare`` exists in the
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``repoze.who.plugins.sql`` module demonstrating this. The
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:class:`SQLAuthenticatorPlugin`\'s ``authenticate`` method will
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return the user id of the user unchanged to ``repoze.who``.
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.. class:: SQLMetadataProviderPlugin(name, query, conn_factory, filter)
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A :class:`SQLMetatadaProviderPlugin` is an ``IMetadataProvider``
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implementation which adds arbitrary metadata to the identity on
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ingress using data from an arbitrary SQL database. The *name*
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argument should be a string. It will be used as a key in the
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identity dictionary. The *query* argument should be a SQL query
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that returns arbitrary data from the database in a form that accepts
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Python-binding style DBAPI arguments. It should expect that a
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``__userid`` value will exist in the dictionary that is bound. The
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SQL query should contain Python-DBAPI style substitution values for
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(at least) ``%(__userid)``, e.g. ``SELECT group FROM groups WHERE
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user_id = %(__userid)``. The *conn_factory* argument should be a
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callable that returns a DBAPI database connection. The *filter*
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argument should be a callable that accepts the result of the DBAPI
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``fetchall`` based on the SQL query. It should massage the data
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into something that will be set in the environment under the *name*
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key.
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Middleware Configuration via Python Code
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========================================
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.. module:: repoze.who.middleware
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.. class:: PluggableAuthenticationMiddleware(app, identifiers, challengers, mdproviders, classifier, challenge_decider [, log_stream=None [, log_level=logging.INFO[, remote_user_key='REMOTE_USER']]])
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The primary method of configuring the ``repoze.who`` middleware is
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to use straight Python code, meant to be consumed by frameworks
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which construct and compose middleware pipelines without using a
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configuration file.
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In the middleware constructor: *app* is the "next" application in
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the WSGI pipeline. *identifiers* is a sequence of ``IIdentifier``
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plugins, *challengers* is a sequence of ``IChallenger`` plugins,
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*mdproviders* is a sequence of ``IMetadataProvider`` plugins. Any
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of these can be specified as the empty sequence. *classifier* is a
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request classifier callable, *challenge_decider* is a challenge
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decision callable. *log_stream* is a stream object (an object with
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a ``write`` method), *log_level* is a numeric value that maps to the
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``logging`` module's notion of log levels, *remote_user_key* is the
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key in which the ``REMOTE_USER`` (userid) value should be placed in
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the WSGI environment for consumption by downstream applications.
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An example configuration which uses the default plugins follows::
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from repoze.who.interfaces import IIdentifier
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from repoze.who.interfaces import IChallenger
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from repoze.who.plugins.basicauth import BasicAuthPlugin
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from repoze.who.plugins.auth_tkt import AuthTktCookiePlugin
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from repoze.who.plugins.cookie import InsecureCookiePlugin
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from repoze.who.plugins.form import FormPlugin
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from repoze.who.plugins.htpasswd import HTPasswdPlugin
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io = StringIO()
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salt = 'aa'
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for name, password in [ ('admin', 'admin'), ('chris', 'chris') ]:
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io.write('%s:%s\n' % (name, password))
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io.seek(0)
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def cleartext_check(password, hashed):
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return password == hashed
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htpasswd = HTPasswdPlugin(io, cleartext_check)
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basicauth = BasicAuthPlugin('repoze.who')
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auth_tkt = AuthTktCookiePlugin('secret', 'auth_tkt')
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form = FormPlugin('__do_login', rememberer_name='auth_tkt')
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form.classifications = { IIdentifier:['browser'],
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IChallenger:['browser'] } # only for browser
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identifiers = [('form', form),('auth_tkt',auth_tkt),('basicauth',basicauth)]
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authenticators = [('htpasswd', htpasswd)]
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challengers = [('form',form), ('basicauth',basicauth)]
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mdproviders = []
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from repoze.who.classifiers import default_request_classifier
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from repoze.who.classifiers import default_challenge_decider
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log_stream = None
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import os
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if os.environ.get('WHO_LOG'):
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log_stream = sys.stdout
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middleware = PluggableAuthenticationMiddleware(
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app,
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identifiers,
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authenticators,
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challengers,
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mdproviders,
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default_request_classifier,
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default_challenge_decider,
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log_stream = log_stream,
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log_level = logging.DEBUG
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)
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return middleware
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The above example configures the repoze.who middleware with:
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- Three ``IIdentifier`` plugins (form auth, auth_tkt cookie, and a
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basic auth plugin). The form auth plugin is set up to fire only
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when the request is a ``browser`` request (as per the combination of
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the request classifier returning ``browser`` and the framework
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checking against the *classifications* attribute of the plugin,
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which limits ``IIdentifier`` and ``IChallenger`` to the ``browser``
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classification only). In this setup, when "identification" needs to
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be performed, the form auth plugin will be checked first (if the
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request is a browser request), then the auth_tkt cookie plugin, then
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the basic auth plugin.
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- One ``IAuthenticator`` plugin: an htpasswd one. This htpasswd
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plugin is configured with two valid username/password combinations:
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chris/chris, and admin/admin. When an username and password is
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found via any identifier, it will be checked against this
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authenticator.
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- Two ``IChallenger`` plugins: the form plugin, then the basic auth
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plugin. The form auth will fire if the request is a ``browser``
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request, otherwise the baisc auth plugin will fire.
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The rest of the middleware configuration is for values like logging
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and the classifier and decider implementations. These use the "stock"
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implementations and values.
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Middleware Configuration via Config File
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========================================
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``repoze.who`` may optionally be configured using a ConfigParser-style
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.INI file. The configuration file has five main types of sections:
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plugin sections, a general section, an identifiers section, an
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authenticators section, and a challengers section. Each "plugin"
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section defines a configuration for a particular plugin. The
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identifiers, authenticators, and challengers sections refer to these
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plugins to form a site configuration. The general section is general
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middleware configuration.
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``repoze.who``'s configuration file can be pointed to within a PasteDeploy
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configuration file ::
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[filter:who]
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use = egg:repoze.who#config
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config_file = %(here)s/who.ini
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log_file = stdout
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log_level = debug
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Below is an example of a configuration file (what ``config_file``
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might point at above ) that might be used to configure the
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``repoze.who`` middleware. A set of plugins are defined, and they are
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referred to by following non-plugin sections.
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In the below configuration, five plugins are defined. The form, and
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basicauth plugins are nominated to act as challenger plugins. The
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form, cookie, and basicauth plugins are nominated to act as
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identification plugins. The htpasswd and sqlusers plugins are
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nominated to act as authenticator plugins. ::
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[plugin:form]
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# identificaion and challenge
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use = repoze.who.plugins.form:make_plugin
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login_form_qs = __do_login
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rememberer_name = cookie
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form = %(here)s/login_form.html
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[plugin:auth_tkt]
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# identification
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use = repoze.who.plugins.auth_tkt:make_plugin
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secret = s33kr1t
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cookie_name = oatmeal
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secure = False
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include_ip = False
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[plugin:basicauth]
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# identification and challenge
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use = repoze.who.plugins.basicauth:make_plugin
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realm = 'sample'
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[plugin:htpasswd]
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# authentication
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use = repoze.who.plugins.htpasswd:make_plugin
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filename = %(here)s/passwd
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check_fn = repoze.who.plugins.htpasswd:crypt_check
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[plugin:sqlusers]
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# authentication
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use = repoze.who.plugins.sql:make_authenticator_plugin
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query = "SELECT userid, password FROM users where login = %(login)s;"
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conn_factory = repoze.who.plugins.sql:make_psycopg_conn_factory
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compare_fn = repoze.who.plugins.sql:default_password_compare
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[plugin:sqlproperties]
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name = properties
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use = repoze.who.plugins.sql:make_metadata_plugin
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query = "SELECT firstname, lastname FROM users where userid = %(__userid)s;"
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filter = my.package:filter_propmd
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conn_factory = repoze.who.plugins.sql:make_psycopg_conn_factory
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[general]
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request_classifier = repoze.who.classifiers:default_request_classifier
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challenge_decider = repoze.who.classifiers:default_challenge_decider
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[identifiers]
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# plugin_name;classifier_name:.. or just plugin_name (good for any)
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plugins =
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form;browser
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auth_tkt
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basicauth
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[authenticators]
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# plugin_name;classifier_name.. or just plugin_name (good for any)
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plugins =
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htpasswd
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sqlusers
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[challengers]
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# plugin_name;classifier_name:.. or just plugin_name (good for any)
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plugins =
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form;browser
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basicauth
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[mdproviders]
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plugins =
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sqlproperties
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The basicauth section configures a plugin that does identification and
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challenge for basic auth credentials. The form section configures a
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plugin that does identification and challenge (its implementation
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defers to the cookie plugin for identification "forget" and "remember"
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duties, thus the "identifier_impl_name" key; this is looked up at
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runtime). The auth_tkt section configures a plugin that does
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identification for cookie auth credentials. The htpasswd plugin
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obtains its user info from a file. The sqlusers plugin obtains its
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user info from a Postgres database.
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The identifiers section provides an ordered list of plugins that are
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willing to provide identification capability. These will be consulted
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in the defined order. The tokens on each line of the ``plugins=`` key
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are in the form "plugin_name;requestclassifier_name:..." (or just
|
"plugin_name" if the plugin can be consulted regardless of the
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classification of the request). The configuration above indicates
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that the system will look for credentials using the form plugin (if
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the request is classified as a browser request), then the cookie
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identifier (unconditionally), then the basic auth plugin
|
(unconditionally).
|
|
The authenticators section provides an ordered list of plugins that
|
provide authenticator capability. These will be consulted in the
|
defined order, so the system will look for users in the file, then in
|
the sql database when attempting to validate credentials. No
|
classification prefixes are given to restrict which of the two plugins
|
are used, so both plugins are consulted regardless of the
|
classification of the request. Each authenticator is called with each
|
set of identities found by the identifier plugins. The first identity
|
that can be authenticated is used to set ``REMOTE_USER``.
|
|
The mdproviders section provides an ordered list of plugins that
|
provide metadata provider capability. These will be consulted in the
|
defined order. Each will have a chance (on ingress) to provide add
|
metadata to the authenticated identity. Our example mdproviders
|
section shows one plugin configured: "sqlproperties". The
|
sqlproperties plugin will add information related to user properties
|
(e.g. first name and last name) to the identity dictionary.
|
|
The challengers section provides an ordered list of plugins that
|
provide challenger capability. These will be consulted in the defined
|
order, so the system will consult the cookie auth plugin first, then
|
the basic auth plugin. Each will have a chance to initiate a
|
challenge. The above configuration indicates that the form challenger
|
will fire if it's a browser request, and the basic auth challenger
|
will fire if it's not (fallback).
|
|
Writing ``repoze.who`` Plugins
|
==============================
|
|
``repoze.who`` can be extended arbitrarily through the creation of
|
plugins. Plugins are of one of four types: identifier plugins,
|
authenticator plugins, metadata provider plugins, and challenge
|
plugins.
|
|
Writing An Identifier Plugin
|
----------------------------
|
|
An identifier plugin (aka an ``IIdentifier`` plugin) must do three
|
things: extract credentials from the request and turn them into an
|
"identity", "remember" credentials, and "forget" credentials.
|
|
Here's a simple cookie identification plugin that does these three
|
things ::
|
|
class InsecureCookiePlugin(object):
|
|
def __init__(self, cookie_name):
|
self.cookie_name = cookie_name
|
|
def identify(self, environ):
|
cookies = get_cookies(environ)
|
cookie = cookies.get(self.cookie_name)
|
|
if cookie is None:
|
return None
|
|
import binascii
|
try:
|
auth = cookie.value.decode('base64')
|
except binascii.Error: # can't decode
|
return None
|
|
try:
|
login, password = auth.split(':', 1)
|
return {'login':login, 'password':password}
|
except ValueError: # not enough values to unpack
|
return None
|
|
def remember(self, environ, identity):
|
cookie_value = '%(login)s:%(password)s' % identity
|
cookie_value = cookie_value.encode('base64').rstrip()
|
from paste.request import get_cookies
|
cookies = get_cookies(environ)
|
existing = cookies.get(self.cookie_name)
|
value = getattr(existing, 'value', None)
|
if value != cookie_value:
|
# return a Set-Cookie header
|
set_cookie = '%s=%s; Path=/;' % (self.cookie_name, cookie_value)
|
return [('Set-Cookie', set_cookie)]
|
|
def forget(self, environ, identity):
|
# return a expires Set-Cookie header
|
expired = ('%s=""; Path=/; Expires=Sun, 10-May-1971 11:59:00 GMT' %
|
self.cookie_name)
|
return [('Set-Cookie', expired)]
|
|
def __repr__(self):
|
return '<%s %s>' % (self.__class__.__name__, id(self))
|
|
.identify
|
~~~~~~~~~
|
|
The ``identify`` method of our InsecureCookiePlugin accepts a single
|
argument "environ". This will be the WSGI environment dictionary.
|
Our plugin attempts to grub through the cookies sent by the client,
|
trying to find one that matches our cookie name. If it finds one that
|
matches, it attempts to decode it and turn it into a login and a
|
password, which it returns as values in a dictionary. This dictionary
|
is thereafter known as an "identity". If it finds no credentials in
|
cookies, it returns None (which is not considered an identity).
|
|
More generally, the ``identify`` method of an ``IIdentifier`` plugin
|
is called once on WSGI request "ingress", and it is expected to grub
|
arbitrarily through the WSGI environment looking for credential
|
information. In our above plugin, the credential information is
|
expected to be in a cookie but credential information could be in a
|
cookie, a form field, basic/digest auth information, a header, a WSGI
|
environment variable set by some upstream middleware or whatever else
|
someone might use to stash authentication information. If the plugin
|
finds credentials in the request, it's expected to return an
|
"identity": this must be a dictionary. The dictionary is not required
|
to have any particular keys or value composition, although it's wise
|
if the identification plugin looks for both a login name and a
|
password information to return at least {'login':login_name,
|
'password':password}, as some authenticator plugins may depend on
|
presence of the names "login" and "password" (e.g. the htpasswd and
|
sql ``IAuthenticator`` plugins). If an ``IIdentifier`` plugin finds
|
no credentials, it is expected to return None.
|
|
An ``IIdentifier`` plugin is also permitted to "preauthenticate" an
|
identity. If the identifier plugin knows that the identity is "good"
|
(e.g. in the case of ticket-based authentication where the userid is
|
embedded into the ticket), it can insert a special key into the
|
identity dictionary: ``repoze.who.userid``. If this key is present in
|
the identity dictionary, no authenticators will be asked to
|
authenticate the identity. This effectively allows an ``IIdentifier``
|
plugin to become an ``IAuthenticator`` plugin when breaking apart the
|
responsibility into two separate plugins is "make-work".
|
Preauthenticated identities will be selected first when deciding which
|
identity to use for any given request. Our cookie plugin doesn't use
|
this feature.
|
|
.remember
|
~~~~~~~~~
|
|
If we've passed a REMOTE_USER to the WSGI application during ingress
|
(as a result of providing an identity that could be authenticated),
|
and the downstream application doesn't kick back with an unauthorized
|
response, on egress we want the requesting client to "remember" the
|
identity we provided if there's some way to do that and if he hasn't
|
already, in order to ensure he will pass it back to us on subsequent
|
requests without requiring another login. The remember method of an
|
``IIdentifier`` plugin is called for each non-unauthenticated
|
response. It is the responsibility of the ``IIdentifier`` plugin to
|
conditionally return HTTP headers that will cause the client to
|
remember the credentials implied by "identity".
|
|
Our InsecureCookiePlugin implements the "remember" method by returning
|
headers which set a cookie if and only if one is not already set with
|
the same name and value in the WSGI environment. These headers will
|
be tacked on to the response headers provided by the downstream
|
application during the response.
|
|
When you write a remember method, most of the work involved is
|
determining *whether or not* you need to return headers. It's typical
|
to see remember methods that compute an "old state" and a "new state"
|
and compare the two against each other in order to determine if
|
headers need to be returned. In our example InsecureCookiePlugin, the
|
"old state" is ``cookie_value`` and the "new state" is ``value``.
|
|
.forget
|
~~~~~~~
|
|
Eventually the WSGI application we're serving will issue a "401
|
Unauthorized" or another status signifying that the request could not
|
be authorized. ``repoze.who`` intercepts this status and calls
|
``IIdentifier`` plugins asking them to "forget" the credentials
|
implied by the identity. It is the "forget" method's job at this
|
point to return HTTP headers that will effectively clear any
|
credentials on the requesting client implied by the "identity"
|
argument.
|
|
Our InsecureCookiePlugin implements the "forget" method by returning
|
a header which resets the cookie that was set earlier by the remember
|
method to one that expires in the past (on my birthday, in fact).
|
This header will be tacked onto the response headers provided by the
|
downstream application.
|
|
Writing an Authenticator Plugin
|
-------------------------------
|
|
An authenticator plugin (aka an ``IAuthenticator`` plugin) must do
|
only one thing (on "ingress"): accept an identity and check if the
|
identity is "good". If the identity is good, it should return a "user
|
id". This user id may or may not be the same as the "login" provided
|
by the user. An ``IAuthenticator`` plugin will be called for each
|
identity found during the identification phase (there may be multiple
|
identities for a single request, as there may be multiple
|
``IIdentifier`` plugins active at any given time), so it may be called
|
multiple times in the same request.
|
|
Here's a simple authenticator plugin that attempts to match an
|
identity against ones defined in an "htpasswd" file that does just
|
that::
|
|
class SimpleHTPasswdPlugin(object):
|
|
def __init__(self, filename):
|
self.filename = filename
|
|
# IAuthenticatorPlugin
|
def authenticate(self, environ, identity):
|
try:
|
login = identity['login']
|
password = identity['password']
|
except KeyError:
|
return None
|
|
f = open(self.filename, 'r')
|
|
for line in f:
|
try:
|
username, hashed = line.rstrip().split(':', 1)
|
except ValueError:
|
continue
|
if username == login:
|
if crypt_check(password, hashed):
|
return username
|
return None
|
|
def crypt_check(password, hashed):
|
from crypt import crypt
|
salt = hashed[:2]
|
return hashed == crypt(password, salt)
|
|
An ``IAuthenticator`` plugin implements one "interface" method:
|
"authentictate". The formal specification for the arguments and
|
return values expected from these methods are available in the
|
``interfaces.py`` file in ``repoze.who`` as the ``IAuthenticator``
|
interface, but let's examine this method here less formally.
|
|
.authenticate
|
~~~~~~~~~~~~~
|
|
The ``authenticate`` method accepts two arguments: the WSGI
|
environment and an identity. Our SimpleHTPasswdPlugin
|
``authenticate`` implementation grabs the login and password out of
|
the identity and attempts to find the login in the htpasswd file. If
|
it finds it, it compares the crypted version of the password provided
|
by the user to the crypted version stored in the htpasswd file, and
|
finally, if they match, it returns the login. If they do not match,
|
it returns None.
|
|
.. note::
|
|
Our plugin's ``authenticate`` method does not assume that the keys
|
``login`` or ``password`` exist in the identity; although it
|
requires them to do "real work" it returns None if they are not
|
present instead of raising an exception. This is required by the
|
``IAuthenticator`` interface specification.
|
|
Writing a Challenger Plugin
|
---------------------------
|
|
A challenger plugin (aka an ``IChallenger`` plugin) must do only one
|
thing on "egress": return a WSGI application which performs a
|
"challenge". A WSGI application is a callable that accepts an
|
"environ" and a "start_response" as its parameters; see "PEP 333" for
|
further definition of what a WSGI application is. A challenge asks
|
the user for credentials.
|
|
Here's an example of a simple challenger plugin::
|
|
from paste.httpheaders import WWW_AUTHENTICATE
|
from paste.httpexceptions import HTTPUnauthorized
|
|
class BasicAuthChallengerPlugin(object):
|
|
def __init__(self, realm):
|
self.realm = realm
|
|
# IChallenger
|
def challenge(self, environ, status, app_headers, forget_headers):
|
head = WWW_AUTHENTICATE.tuples('Basic realm="%s"' % self.realm)
|
if head[0] not in forget_headers:
|
head = head + forget_headers
|
return HTTPUnauthorized(headers=head)
|
|
Note that the plugin implements a single "interface" method:
|
"challenge". The formal specification for the arguments and return
|
values expected from this method is available in the "interfaces.py"
|
file in ``repoze.who`` as the ``IChallenger`` interface. This method
|
is called when ``repoze.who`` determines that the application has
|
returned an "unauthorized" response (e.g. a 401). Only one challenger
|
will be consulted during "egress" as necessary (the first one to
|
return a non-None response).
|
|
.challenge
|
~~~~~~~~~~
|
|
The challenge method takes environ (the WSGI environment), 'status'
|
(the status as set by the downstream application), the "app_headers"
|
(headers returned by the application), and the "forget_headers"
|
(headers returned by all participating ``IIdentifier`` plugins whom
|
were asked to "forget" this user).
|
|
Our BasicAuthChallengerPlugin takes advantage of the fact that the
|
HTTPUnauthorized exception imported from paste.httpexceptions can be
|
used as a WSGI application. It first makes sure that we don't repeat
|
headers if an identification plugin has already set a
|
"WWW-Authenticate" header like ours, then it returns an instance of
|
HTTPUnauthorized, passing in merged headers. This will cause a basic
|
authentication dialog to be presented to the user.
|
|
Writing a Metadata Provider Plugin
|
----------------------------------
|
|
A metadata provider plugin (aka an ``IMetadataProvider`` plugin) must
|
do only one thing (on "ingress"): "scribble" on the identity
|
dictionary provided to it when it is called. An ``IMetadataProvider``
|
plugin will be called with the final "best" identity found during the
|
authentication phase, or not at all if no "best" identity could be
|
authenticated. Thus, each ``IMetadataProvider`` plugin will be called
|
exactly zero or one times during a request.
|
|
Here's a simple metadata provider plugin that provides "property"
|
information from a dictionary::
|
|
_DATA = {
|
'chris': {'first_name':'Chris', 'last_name':'McDonough'} ,
|
'whit': {'first_name':'Whit', 'last_name':'Morriss'}
|
}
|
|
class SimpleMetadataProvider(object):
|
|
def add_metadata(self, environ, identity):
|
userid = identity.get('repoze.who.userid')
|
info = _DATA.get(userid)
|
if info is not None:
|
identity.update(info)
|
|
.add_metadata
|
~~~~~~~~~~~~~
|
|
Arbitrarily add information to the identity dict based in other data
|
in the environment or identity. Our plugin adds ``first_name`` and
|
``last_name`` values to the identity if the userid matches ``chris``
|
or ``whit``.
|
|
Interfaces
|
==========
|
|
.. module:: repoze.who.interfaces
|
|
.. autointerface:: repoze.who.interfaces.IRequestClassifier
|
:members:
|
|
.. autointerface:: repoze.who.interfaces.IChallengeDecider
|
:members:
|
|
.. autointerface:: repoze.who.interfaces.IIdentifier
|
:members:
|
|
.. autointerface:: repoze.who.interfaces.IAuthenticator
|
:members:
|
|
.. autointerface:: repoze.who.interfaces.IChallenger
|
:members:
|
|
.. autointerface:: repoze.who.interfaces.IMetadataProvider
|
:members:
|
