| | |
| | | repoze.pam |
| | | ``repoze.who`` -- WSGI Authentication Middleware / API |
| | | ====================================================== |
| | | |
| | | Overview |
| | | -------- |
| | | |
| | | repoze.pam (Pluggable Authentication Middleware) is an |
| | | identification and authentication framework for WSGI. |
| | | ``repoze.who`` is an identification and authentication framework |
| | | for arbitrary WSGI applications. ``repoze.who`` can be configured |
| | | either as WSGI middleware or as an API for use by an application. |
| | | |
| | | Description |
| | | |
| | | repoze.pam's ideas are largely culled from Zope 2's Pluggable |
| | | Authentication Service (PAS) (but repoze.pam is not dependent on |
| | | Zope 2 in any way). Unlike PAS, it provides no facilities for |
| | | creating user objects, assigning roles or groups to users, |
| | | retrieving or changing user properties, or enumerating users, |
| | | groups, or roles. These responsibilities are assumed to be the |
| | | domain of the WSGI application you're serving. It also provides no |
| | | facility for authorization (ensuring whether a user can or cannot |
| | | perform the operation implied by the request). This is also the |
| | | domain of the WSGI application. |
| | | ``repoze.who`` is inspired by Zope 2's Pluggable Authentication |
| | | Service (PAS) (but ``repoze.who`` is not dependent on Zope in any |
| | | way; it is useful for any WSGI application). It provides no facility |
| | | for authorization (ensuring whether a user can or cannot perform the |
| | | operation implied by the request). This is considered to be the |
| | | domain of the WSGI application. |
| | | |
| | | It attemtps to reuse implementations from paste.auth for some of its |
| | | functionality. |
| | | |
| | | Middleware Responsibilities |
| | | |
| | | repoze.pam's middleware has one major function on ingress: it |
| | | conditionally places identification and authentication information |
| | | (including a REMOTE_USER value) into the WSGI environment and allows |
| | | the request to continue to a downstream WSGI application. |
| | | |
| | | repoze.pam's middleware has one major function on egress: it |
| | | examines the headers set by the downstream application, the WSGI |
| | | environment, or headers supplied by other plugins and conditionally |
| | | challenges for credentials. |
| | | |
| | | PasteDeploy Configuration |
| | | |
| | | Classifiers |
| | | |
| | | repoze.pam "classifies" the request on middleware ingress. Request |
| | | classification happens before identification and authentication. A |
| | | request from a browser might be classified a different way that a |
| | | request from an XML-RPC client. repoze.pam uses request classifiers |
| | | to decide which other components to consult during subsequent |
| | | identification, authentication, and challenge steps. Plugins are |
| | | free to advertise themselves as willing to participate in |
| | | identification and authorization for a request based on this |
| | | classification. |
| | | |
| | | The classification system is pluggable. repoze.pam provides a |
| | | default classifier that you may use. You may extend the |
| | | classification system by making repoze.pam aware of a different |
| | | classifier implementation. |
| | | |
| | | Plugins |
| | | |
| | | repoze.pam is designed around the concept of plugins. Plugins are |
| | | instances that are willing to perform one or more identification- |
| | | and/or authentication-related duties. When you register a plugin, |
| | | you register a plugin factory, which is a callable that accepts |
| | | configuration parameters. The callable must return an instance of a |
| | | plugin when called. Each plugin can be configured arbitrarily using |
| | | values in a repoze.pam-specific configuration file. |
| | | |
| | | repoze.pam consults the set of configured plugins when it intercepts |
| | | a WSGI request, and gives some subset of them a chance to influence |
| | | what is added to the WSGI environment. |
| | | |
| | | Request (Ingress) Stages |
| | | |
| | | repoze.pam performs the following operations in the following order |
| | | during middleware ingress: |
| | | |
| | | 1. Request Classification |
| | | |
| | | The WSGI environment is examined and the request is classified |
| | | into one "type" of request. The callable named as |
| | | 'request_classifer=' within the '[general]' section is used to |
| | | perform the classification. It returns a value that is |
| | | considered to be the request classification. |
| | | |
| | | 2. Identification |
| | | |
| | | Identifiers which nominate themselves as willing to extract data |
| | | for a particular class of request (as provided by the request |
| | | classifier) will be consulted to retrieve credentials data from |
| | | the environment. For example, a basic auth identifier might use |
| | | the HTTP_AUTHORIZATION header to find login and password |
| | | information. Identifiers are also responsible for providing |
| | | header information to set and remove authentication information |
| | | in the response. |
| | | |
| | | 3. Authentication |
| | | |
| | | Authenticators which nominate themselves as willing to |
| | | authenticate for a particular class of request will be consulted |
| | | to compare information provided by the identification plugins |
| | | that returned credentials. For example, an htpasswd |
| | | authenticator might look in a file for a user record matching |
| | | any of the identities. If it finds one, and if the password |
| | | listed in the record matches the password provided by an |
| | | identity, the userid of the user would be returned (which would |
| | | be the same as the login name). |
| | | |
| | | Response (Egress) Stages |
| | | |
| | | repoze.pam performs the following operations in the following order |
| | | during middleware egress: |
| | | |
| | | 1. Challenge Decision |
| | | |
| | | The WSGI environment and the status and headers returned by the |
| | | downstream application may be examined to determine whether a |
| | | challenge is required. Typically, only the status is used (if |
| | | it starts with "401 ", a challenge is required). This behavior |
| | | is pluggable. |
| | | |
| | | 2. Challenge |
| | | |
| | | Challengers which nominate themselves as willing to execute a |
| | | challenge for a particular class of request (as provided by the |
| | | classifier) will be consulted, and one will be chosen to perform |
| | | a challenge. A challenger plugin can use application-returned |
| | | headers, the WSGI environment, and other items to determine what |
| | | sort of operation should be performed to actuate the challenge. |
| | | Note that repoze.pam defers to the identifier plugin which |
| | | provided the identity (if any) to reset credentials at challenge |
| | | time; this is not the responsibility of the challenger. |
| | | |
| | | Plugin Types |
| | | |
| | | Identifier Plugins |
| | | |
| | | You can register a plugin as willing to act as an "identifier". |
| | | An identifier examines the WSGI environment and attempts to |
| | | extract credentials from the environment. These credentials are |
| | | used by authenticator plugins to perform authentication. |
| | | |
| | | Authenticator Plugins |
| | | |
| | | You may register a plugin as willing to act as an "authenticator". |
| | | Authenticator plugins are responsible for resolving a set of |
| | | credentials provided by an identifier plugin into a user id. |
| | | Typically, authenticator plugins will perform a lookup into a |
| | | database or some other persistent store, check the provided |
| | | credentials against the stored data, and return a user id if the |
| | | credentials can be validated. |
| | | |
| | | The user id provided by an authenticator is eventually passed to |
| | | downstream WSGI applications in the "REMOTE_USER' environment |
| | | variable. |
| | | |
| | | Challenger Plugins |
| | | |
| | | You may register a plugin as willing to act as a "challenger". |
| | | Challenger plugins are responsible for initiating a challenge to |
| | | the requesting user. Challenger plugins are invoked by repoze.pam |
| | | when it decides a challenge is necessary. A challenge might |
| | | consist of displaying a form or presenting the user with a basic |
| | | or digest authentication dialog. |
| | | |
| | | Configuration File Example |
| | | |
| | | repoze.pam is configured using a ConfigParser-style .INI file. The |
| | | configuration file has five main types of sections: plugin sections, |
| | | a general section, an identifiers section, an authenticators section, |
| | | and a challengers section. Each "plugin" section defines a |
| | | configuration for a particular plugin. The identifiers, |
| | | authenticators, and challengers sections refer to these plugins to |
| | | form a site configuration. The general section is general middleware |
| | | configuration. |
| | | |
| | | Example repoze.pam Configuration File (*NOTE: SCIENCE FICTION, not yet |
| | | implemented!*) |
| | | |
| | | repoze.pam is designed to be used within a PasteDeploy configuration |
| | | file: |
| | | |
| | | [filter:pam] |
| | | use = egg:repoze.pam#pam |
| | | config_file = %(here)s/pam.ini |
| | | |
| | | Below is an example of a configuration file that might be used to |
| | | configure the repoze.pam middleware. A set of plugins are defined, |
| | | and they are referred to by following non-plugin sections. |
| | | |
| | | In the below configuration, five plugins are defined. The form, and |
| | | basicauth plugins are nominated to act as challenger plugins. The |
| | | form, cookie, and basicauth plugins are nominated to act as |
| | | identification plugins. The htpasswd and sqlusers plugins are |
| | | nominated to act as authenticator plugins. |
| | | |
| | | [plugin:form] |
| | | # identificaion and challenge |
| | | login_form_qs = __do_login |
| | | identifier_impl_name = cookie |
| | | |
| | | [plugin:cookie] |
| | | # identification |
| | | use = egg:repoze.pam#cookie |
| | | cookie_name = repoze.pam.auth |
| | | |
| | | [plugin:basicauth] |
| | | # identification and challenge |
| | | use = egg:repoze.pam#basicauth |
| | | realm = repoze |
| | | |
| | | [plugin:htpasswd] |
| | | # authentication |
| | | use = egg:repoze.pam#htpasswd |
| | | filename = %(here)s/users.htpasswd |
| | | check_fn = egg:repoze.pam#crypt_check |
| | | |
| | | [plugin:sqlusers] |
| | | # authentication |
| | | use = egg:repoze.pam#squsersource |
| | | db = sqlite://database?user=foo&pass=bar |
| | | get_userinfo = select id, password from users |
| | | check_fn = egg:repoze.pam#crypt_check |
| | | |
| | | [general] |
| | | request_classifier = egg:repoze.pam#defaultrequestclassifier |
| | | challenge_decider = egg:repoze.pam#defaultchallengedecider |
| | | |
| | | [identifiers] |
| | | # plugin_name:classifier_name:.. or just plugin_name (good for any) |
| | | plugins = |
| | | form:browser |
| | | cookie |
| | | basicauth |
| | | |
| | | [authenticators] |
| | | # plugin_name:classifier_name.. or just plugin_name (good for any) |
| | | plugins = |
| | | htpasswd |
| | | sqlusers |
| | | |
| | | [challengers] |
| | | # plugin_name:classifier_name:.. or just plugin_name (good for any) |
| | | plugins = |
| | | form:browser |
| | | basicauth |
| | | |
| | | Further Description of Example Config |
| | | |
| | | The basicauth section configures a plugin that does identification |
| | | and challenge for basic auth credentials. The form section |
| | | configures a plugin that does identification and challenge (its |
| | | implementation defers to the cookie plugin for identification |
| | | "forget" and "remember" duties, thus the "identifier_impl_name" key; |
| | | this is looked up at runtime). The cookie section configures a |
| | | plugin that does identification for cookie auth credentials. The |
| | | htpasswd plugin obtains its user info from a file. The sqlusers |
| | | plugin obtains its user info from a sqlite database. |
| | | |
| | | The identifiers section provides an ordered list of plugins that are |
| | | willing to provide identification capability. These will be |
| | | consulted in the defined order. The tokens on each line of the |
| | | 'plugins=' key are in the form |
| | | "plugin_name:requestclassifier_name:..." (or just "plugin_name" if |
| | | the plugin can be consulted regardless of the classification of the |
| | | request). The configuration above indicates that the system will |
| | | look for credentials using the form plugin (if the request is |
| | | classified as a browser request), then the cookie 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 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, based |
| | | on the response classification, 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 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)) |
| | | |
| | | Note that the plugin implements three "interface" methods: |
| | | "identify", "forget" and "remember". The formal specification for |
| | | the arguments and return values expected from these methods are |
| | | available in the "interfaces.py" file in repoze.pam as the |
| | | 'IIdentifier' interface, but let's examine them less formally one at |
| | | a time. |
| | | |
| | | identify(environ) -- |
| | | |
| | | 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 IP-address-based |
| | | authentication, or ticket-based authentication), it can insert a |
| | | special key into the identity dictionary: 'repoze.pam.userid'. If |
| | | this key is present in the identity dictionary, no authenticators |
| | | will be asked to authenticate the identity. |
| | | |
| | | remember(environ, identity) -- |
| | | |
| | | 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. |
| | | |
| | | forget(environ, identity) -- |
| | | |
| | | Eventually the WSGI application we're serving will issue a "401 |
| | | Unauthorized" or another status signifying that the request could |
| | | not be authorized. repoze.pam 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) |
| | | |
| | | Note that the plugin implements a single "interface" method: |
| | | "authenticate". The formal specification for the arguments and |
| | | return values expected from this method is available in the |
| | | "interfaces.py" file in repoze.pam as the 'IAuthenticator' |
| | | interface, but we can explore this a little further here. |
| | | |
| | | 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. |
| | | |
| | | Writing a Challenger Plugin |
| | | |
| | | A challenger plugin (aka an IChallenger plugin) must do only one |
| | | thing (on "egress"): return a WSGI application (see PEP 333 for the |
| | | definition of a WSGI application) which performs a "challenge." 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.pam as the 'IChallenger' interface. This method is |
| | | called when repoze.pam 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). 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. |
| | | |
| | | Interfaces |
| | | |
| | | See the module repoze.pam.interfaces. |
| | | |
| | | See the ``docs`` subdirectory of this package (also available at least |
| | | provisionally at http://static.repoze.org/whodocs) for more |
| | | information. |