Provided by: libcatalyst-modules-perl_47_all 
NAME
Catalyst::Plugin::Authentication::Internals - All about authentication Stores and
Credentials
INTRODUCTION
Catalyst::Plugin::Authentication provides a standard authentication interface to
application developers using the Catalyst framework. It is designed to allow application
developers to use various methods of user storage and credential verification. It is also
designed to provide for minimal change to the application when switching between different
storage and credential verification methods.
While Catalyst::Plugin::Authentication provides the interface to the application
developer, the actual work of verifying the credentials and retrieving users is delegated
to separate modules. These modules are called Credentials and storage backends, or Stores,
respectively. For authentication to function there must be at least one credential and one
store. A pairing of a store and a credential is referred to as a Realm. There may be any
number of realms defined for an application, though most applications will not require
more than one or two.
The details of using this module can be found in the Catalyst::Plugin::Authentication
documentation.
What follows is an explanation of how the module functions internally and what is required
to implement a credential or a store.
OVERVIEW
There are two main entry points you need to be aware of when writing a store or credential
module. The first is initialization and the second is during the actual call to the
Catalyst application's authenticate method.
A simplified description of the authentication process follows:
Initialization
Realm Setup - for each realm:
1) The Realm is instantiated using new() method
2) The Store is instantiated using new() method
3) The Credential Instantiated using new() method
4) Credential and Store objects tied to realm for use during requests
Authentication
"$c->authenticate( $userinfo, $realm )" called
1) Credential object retrieved for realm provided
2) Credential's authenticate() method called with authinfo and realm object for
current realm
The realm object and the authinfo hash are provided to the credential object's
authenticate call. In most cases the credential object will attempt to
retrieve a user using the realm's find_user() method, which by default relays
the call directly to the Store's find_user() method. It will then usually
compare the retrieved user's information with the information provided in the
$authinfo hash. This is how the default 'Password' credential functions. If
the credentials match, the authenticate() method should return a user object.
3) User object stored in session
If the user object supports session storage, the successfully authenticated
user will be placed in session storage. This is done by calling the realm
object's persist_user() method. The persist_user() routine by default calls
the Store's for_session() method, which should return serialized data (IE a
scalar). This serialized data is passed back to the store via the
from_session() method, so the data should contain enough information for the
store to recreate / reload the user.
Sessions - Per-Request operations
When any user-related activity occurs, and $c->authenticate has not yet been called,
the Catalyst::Plugin::Authentication module will attempt to restore the persisted user
(normally from the session if one is available). There is only one step in this
process:
1) Store object's from_session() is called
The serialized data previously returned by the store's for_session() method is
provided to the from_session() method. The from_session() method should return a valid
user object.
Note that the for_session() is only called during the original $c->authenticate()
call, so if changes are made to the user that need to be reflected in your session
data, you will want to call the $c->persist_user() method - which will perform the
session storage process again (complete with call to for_session()).
More detailed information about these processes is below.
INITIALIZATION
When the authentication module is loaded, it reads it's configuration to determine the
realms to set up for the application and which realm is to be the default. For each realm
defined in the application's config, Catalyst::Plugin::Authentication instantiates both a
new credential object and a new store object. See below for the details of how credentials
and stores are instantiated.
NOTE: The instances created will remain active throughout the entire lifetime of the
application, and so should be relatively lightweight. Care should be taken to ensure that
they do not grow, or retain information per request, because they will be involved in each
authentication request and could therefore substantially hurt memory consumption over
time.
AUTHENTICATION
When "$c->authenticate()" is called from within an application, the objects created in the
initialization process come into play. "$c->authenticate()" takes two arguments. The
first is a hash reference containing all the information available about the user. This
will be used to locate the user in the store and verify the user's credentials. The second
argument is the realm to authenticate against. If the second argument is omitted, the
default realm is assumed.
The main authentication module then locates the credential and store objects for the realm
specified and calls the credential object's "authenticate()" method. It provides three
arguments, first the application object, or $c, then a reference to the store object, and
finally the hashref provided in the "$c->authenticate" call. The main authentication
module expects the return value to be a reference to a user object upon successful
authentication. If it receives anything aside from a reference, it is considered to be an
authentication failure. Upon success, the returned user is marked as authenticated and the
application can act accordingly, using "$c->user" to access the authenticated user, etc.
Astute readers will note that the main Catalyst::Plugin::Authentication module does not
interact with the store in any way, save for passing a reference to it to the credential.
This is correct. The credential object is responsible for obtaining the user from the
provided store using information from the userinfo hashref and/or data obtained during the
credential verification process.
WRITING A STORE
There are two parts to an authentication store, the store object and the user object.
STORAGE BACKEND
Writing a store is actually quite simple. There are only five methods that must be
implemented. They are:
new() - instantiates the store object
find_user() - locates a user using data contained in the hashref
for_session() - prepares a user to be stored in the session
from_session() - does any restoration required when obtaining a user from the session
user_supports() - provides information about what the user object supports
STORE METHODS
new( $config, $app, $realm )
The "new()" method is called only once, during the setup process of
Catalyst::Plugin::Authentication. The first argument, $config, is a hash reference
containing the configuration information for the store module. The second argument is
a reference to the Catalyst application.
Note that when new() is called, Catalyst has not yet loaded the various controller and
model classes, nor is it definite that other plugins have been loaded, so your new()
method must not rely on any of those being present. If any of this is required for
your store to function, you should defer that part of initialization until the first
method call.
The "new()" method should return a blessed reference to your store object.
find_user( $authinfo, $c )
This is the workhorse of any authentication store. It's job is to take the information
provided to it via the $authinfo hashref and locate the user that matches it. It
should return a reference to a user object. A return value of anything else is
considered to mean no user was found that matched the information provided.
How "find_user()" accomplishes it's job is entirely up to you, the author, as is what
$authinfo is required to contain. Many stores will simply use a username element in
$authinfo to locate the user, but more advanced functionality is possible and you may
bend the $authinfo to your needs. Be aware, however, that both Credentials and Stores
usually work with the same $authinfo hash, so take care to avoid overlapping element
names.
Please note that this routine may be called numerous times in various circumstances,
and that a successful match for a user here does NOT necessarily constitute successful
authentication. Your store class should never assume this and in most cases $c should
not be modified by your store object.
for_session( $c, $user )
This method is responsible for preparing a user object for storage in the session. It
should return information that can be placed in the session and later used to restore
a user object (using the "from_session()" method). It should therefore ensure that
whatever information provided can be used by the "from_session()" method to locate the
unique user being saved. Note that there is no guarantee that the same Catalyst
instance will receive both the "for_session()" and "from_session()" calls. You should
take care to provide information that can be used to restore a user, regardless of the
current state of the application. A good rule of thumb is that if "from_session()"
can revive the user with the given information even if the Catalyst application has
just started up, you are in good shape.
from_session( $c, $frozenuser )
This method is called whenever a user is being restored from the session. $frozenuser
contains the information that was stored in the session for the user. This will under
normal circumstances be the exact data your store returned from the previous call to
"for_session()". "from_session()" should return a valid user object.
user_supports( $feature, ... )
This method allows credentials and other objects to inquire as to what the underlying
user object is capable of. This is pretty-well free-form and the main purpose is to
allow graceful integration with credentials and applications that may provide advanced
functionality based on whether the underlying user object can do certain things. In
most cases you will want to pass this directly to the underlying user class'
"supports" method. Note that this is used as a class method against the user class and
therefore must be able to function without an instantiated user object.
OPTIONAL STORE METHODS
If you want your store to be able to auto- create users, then you can implement these
methods:
auto_update_user( $authinfo, $c, $res )
This method is called if the realm's auto_update_user setting is true.
auto_create_user( $authinfo, $c )
This method is called if the realm's auto_create_user setting is true.
USER OBJECT
The user object is an important piece of your store module. It will be the part of the
system that the application developer will interact with most. As such, the API for the
user object is very rigid. All user objects MUST inherit from
Catalyst::Authentication::User.
USER METHODS
The routines required by the Catalyst::Plugin::Authentication plugin are below. Note that
of these, only get_object is strictly required, as the Catalyst::Authentication::User base
class contains reasonable implementations of the rest. If you do choose to implement only
the "get_object()" routine, please read the base class code and documentation so that you
fully understand how the other routines will be implemented for you.
Also, your user object can implement whatever additional methods you require to provide
the functionality you need. So long as the below are implemented, and you don't overlap
the base class' methods with incompatible routines, you should experience no problems.
id( )
The "id()" method should return a unique id (scalar) that can be used to retreive this
user from the store. Often this will be provided to the store's "find_user()" routine
as "id => $user->id" so you should ensure that your store's "find_user()" can cope
with that.
supports( $feature, $subfeature ... )
This method checks to see if the user class supports a particular feature. It is
implemented such that each argument provides a subfeature of the previous argument. In
other words, passing 'foo', 'bar' would return true if the user supported the 'foo'
feature, and the 'bar' feature of 'foo'. This is implemented in
Catalyst::Authentication::User, so if your class inherits from that, you do not need
to implement this and can instead implement supported_features().
Note: If you want the authentication module to be able to save your user in the
session you must return true when presented with the feature 'session'.
supported_features( )
This method should return a hashref of features supported by the user class. This is
for more flexible integration with some Credentials / applications. It is not required
that you support anything, and returning "undef" is perfectly acceptable and in most
cases what you will do.
get( $fieldname )
This method should return the value of the field matching fieldname provided, or undef
if there is no field matching that fieldname. In most cases this will access the
underlying storage mechanism for the user data and return the information. This is
used as a standard method of accessing an authenticated user's data, and MUST be
implemented by all user objects.
Note: There is no equivalent 'set' method. Each user class is likely to vary greatly
in how data must be saved and it is therefore impractical to try to provide a standard
way of accomplishing it. When an application developer needs to save data, they should
obtain the underlying object / data by calling get_object, and work with it directly.
get_object( )
This method returns the underlying user object. If your user object is backed by
another object class, this method should return that underlying object. This allows
the application developer to obtain an editable object. Generally speaking this will
only be done by developers who know what they are doing and require advanced
functionality which is either unforeseen or inconsistent across user classes. If your
object is not backed by another class, or you need to provide additional intermediate
functionality, it is perfectly reasonable to return $self.
WRITING A CREDENTIAL
Compared to writing a store, writing a credential is very simple. There is only one class
to implement, and it consists of only two required routines. They are:
new() - instantiates the credential object
authenticate() - performs the authentication and returns a user object
CREDENTIAL METHODS
new( $config, $app, $realm )
Like the Store method of the same name, the "new()" method is called only once, during
the setup process of Catalyst::Plugin::Authentication. The first argument, $config, is
a hash reference containing the configuration information for the credential module.
The second argument is a reference to the Catalyst application. $realm is the
instantiated Realm object, which you may use to access realm routines - such as
find_user.
Again, when the credential's new() method is called, Catalyst has not yet loaded the
various controller and model classes.
The new method should perform any necessary setup required and instantiate your
credential object. It should return your instantiated credential.
authenticate( $c, $realm, $authinfo )
This is the workhorse of your credential. When $c->authenticate() is called the
Catalyst::Plugin::Authentication module retrieves the realm object and passes it,
along with the $authinfo hash to your credential's authenticate method. Your module
should use the $authinfo hash to obtain the user from the realm passed, and then
perform any credential verification steps necessary to authenticate the user. This
method should return the user object returned by the authentication store if
credential verification succeeded. It should return undef on failure.
How your credential module performs the credential verification is entirely up to you.
In most cases, the credential will retrieve a user from the store first (using the
stores find_user() method), and then validate the user's information. However, this
does not have to be the case.
It is perfectly acceptable for your credential to perform other tasks prior to
attempting to retrieve the user from the store. It may also make sense for your
credential to perform activities which help to locate the user in question, for
example, finding a user id based on an encrypted token. In these scenarios, the
$authinfo hash passed to find_user() can be different than that which is passed in to
$c->authenticate(). Once again this is perfectly acceptable if it makes sense for your
credential, though you are strongly advised to note this behavior clearly in your
credential's documentation - as application authors are almost certainly expecting the
user to be found using the information provided to $c->authenticate().
Look at the Catalyst::Authentication::Credential::Password module source to see this
in action. In order to avoid possible mismatches between the encrypted and
unencrypted passwords, the password credential actually removes the provided password
from the authinfo array. It does this because, in many cases, the store's password
field will be encrypted in some way, and the password passed to $c->authenticate is
almost certainly in plaintext.
NOTE: You should always assume that a store is going to use all the information passed
to it to locate the user in question. If there are fields in the $authinfo hash that
you are sure are specific to your credential, you may want to consider removing them
before user retrieval. A better solution is to place those arguments that are
specific to your credential within their own subhash named after your module.
The Catalyst::Authentication::Store::DBIx::Class module does this in order to
encapsulate arguments intended specifically for that module. See the
Catalyst::Authentication::Store::DBIx::Class::User source for details.
AUTHORS
Jay Kuri, "jayk@cpan.org"
COPYRIGHT & LICENSE
Copyright (c) 2005 the aforementioned authors. All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.18.1 2012-Catalyst::Plugin::Authentication::Internals(3pm)