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1 | |
2 | =head1 NAME |
3 | |
4 | Catalyst::Plugin::Authentication::Internals - All about authentication Stores and Credentials |
5 | |
6 | =head1 INTRODUCTION |
7 | |
8 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> provides |
9 | a standard authentication interface to application developers using the |
10 | Catalyst framework. It is designed to allow application developers to use |
11 | various methods of user storage and credential verification. It is also |
12 | designed to provide for minimal change to the application when switching |
13 | between different storage and credential verification methods. |
14 | |
15 | While L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> |
16 | provides the interface to the application developer, the actual work of |
17 | verifying the credentials and retrieving users is delegated to separate |
18 | modules. These modules are called B<Credentials> and storage backends, or |
19 | B<Stores>, respectively. For authentication to function there must be at least |
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20 | one credential and one store. A pairing of a store and a credential |
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21 | is referred to as a B<Realm>. There may be any number of realms defined for an |
22 | application, though most applications will not require more than one or two. |
23 | |
24 | The details of using this module can be found in the |
25 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> |
26 | documentation. |
27 | |
28 | What follows is an explanation of how the module functions internally and what |
29 | is required to implement a credential or a store. |
30 | |
31 | =head1 OVERVIEW |
32 | |
33 | There are two main entry points you need to be aware of when writing a store |
34 | or credential module. The first is initialization and the second is during the |
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35 | actual call to the Catalyst application's authenticate method. |
36 | |
37 | A simplified description of the authentication process follows: |
38 | |
39 | |
40 | |
41 | B<Initialization> |
42 | |
43 | =over 4 |
44 | |
45 | B<Realm Setup> - for each realm: |
46 | |
47 | =over 4 |
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48 | 1) The Realm is instantiated using new() method |
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49 | |
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50 | 2) The Store is instantiated using new() method |
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51 | |
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52 | 3) The Credential Instantiated using new() method |
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53 | |
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54 | 4) Credential and Store objects tied to realm for use during requests |
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55 | |
56 | =back |
57 | |
58 | =back |
59 | |
60 | B<Authentication> |
61 | |
62 | =over 4 |
63 | |
64 | C<< $c->authenticate( $userinfo, $realm ) >> called |
65 | |
66 | =over 4 |
67 | |
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68 | 1) Credential object retrieved for realm provided |
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69 | |
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70 | 2) Credential's authenticate() method called with authinfo and realm object for current realm |
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71 | |
72 | =over 4 |
73 | |
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74 | The realm object and the authinfo hash are provided to the credential object's |
75 | authenticate call. In most cases the credential object will attempt to |
76 | retrieve a user using the realm's find_user() method, which by default relays |
77 | the call directly to the Store's find_user() method. It will then usually |
78 | compare the retrieved user's information with the information provided in the |
79 | $authinfo hash. This is how the default 'Password' credential functions. If |
80 | the credentials match, the authenticate() method should return a user object. |
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81 | |
82 | =back |
83 | |
84 | 3) User object stored in session |
85 | |
86 | =over 4 |
87 | |
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88 | If the user object supports session storage, the successfully authenticated |
89 | user will be placed in session storage. This is done by calling the realm |
90 | object's save_user_in_session() method. The save_user_in_session() routine by |
91 | default calls the Store's for_session() method, which should return serialized |
92 | data (IE a scalar). This serialized data is passed back to the store via the |
93 | from_session() method, so the data should contain enough information for the |
94 | store to recreate / reload the user. |
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95 | |
96 | =back |
97 | |
98 | =back |
99 | |
100 | =back |
101 | |
102 | B<Sessions> - Per-Request operations |
103 | |
104 | =over 4 |
105 | |
106 | When any user-related activity occurs, and $c->authenticate has not |
107 | yet been called, the Catalyst::Plugin::Authentication module will |
108 | attempt to restore the user from the session (if one is available). |
109 | There is only one step in this process: |
110 | |
111 | =over 4 |
112 | |
113 | 1) Store object's from_session() is called |
114 | |
115 | =back |
116 | |
117 | The serialized data previously returned by the store's for_session() |
118 | method is provided to the from_session() method. The from_session() |
119 | method should return a valid user object. |
120 | |
121 | Note that the for_session() is only called during the original |
122 | $c->authenticate() call, so if changes are made to the user that need |
123 | to be reflected in your session data, you will want to call the |
124 | $c->save_user_in_session() method - which will perform the session |
125 | storage process again (complete with call to for_session()). |
126 | |
127 | =back |
128 | |
129 | More detailed information about these processes is below. |
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130 | |
131 | =head2 INITIALIZATION |
132 | |
133 | When the authentication module is loaded, it reads it's configuration to |
134 | determine the realms to set up for the application and which realm is to be |
135 | the default. For each realm defined in the application's config, |
136 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> |
137 | instantiates both a new credential object and a new store object. See below |
138 | for the details of how credentials and stores are instantiated. |
139 | |
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140 | B<NOTE>: The instances created will remain active throughout the entire |
141 | lifetime of the application, and so should be relatively lightweight. |
142 | Care should be taken to ensure that they do not grow, or retain |
143 | information per request, because they will be involved in each |
144 | authentication request and could therefore substantially |
145 | hurt memory consumption over time. |
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146 | |
147 | =head2 AUTHENTICATION |
148 | |
149 | When C<$c-E<gt>authenticate()> is called from within an application, the |
150 | objects created in the initialization process come into play. |
151 | C<$c-E<gt>authenticate()> takes two arguments. The first is a hash reference |
152 | containing all the information available about the user. This will be used to |
153 | locate the user in the store and verify the user's credentials. The second |
154 | argument is the realm to authenticate against. If the second argument is |
155 | omitted, the default realm is assumed. |
156 | |
157 | The main authentication module then locates the credential and store objects |
158 | for the realm specified and calls the credential object's C<authenticate()> |
159 | method. It provides three arguments, first the application object, or C<$c>, |
160 | then a reference to the store object, and finally the hashref provided in the |
161 | C<$c-E<gt>authenticate> call. The main authentication module expects the |
162 | return value to be a reference to a user object upon successful |
163 | authentication. If it receives anything aside from a reference, it is |
164 | considered to be an authentication failure. Upon success, the returned user is |
165 | marked as authenticated and the application can act accordingly, using |
166 | C<$c-E<gt>user> to access the authenticated user, etc. |
167 | |
168 | Astute readers will note that the main |
169 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> module |
170 | does not interact with the store in any way, save for passing a reference to |
171 | it to the credential. This is correct. The credential object is responsible |
172 | for obtaining the user from the provided store using information from the |
173 | userinfo hashref and/or data obtained during the credential verification |
174 | process. |
175 | |
176 | =head1 WRITING A STORE |
177 | |
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178 | There are two parts to an authentication store, the store object and the user object. |
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179 | |
180 | =head2 STORAGE BACKEND |
181 | |
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182 | Writing a store is actually quite simple. There are only five methods |
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183 | that must be implemented. They are: |
184 | |
185 | new() - instantiates the store object |
186 | find_user() - locates a user using data contained in the hashref |
187 | for_session() - prepares a user to be stored in the session |
188 | from_session() - does any restoration required when obtaining a user from the session |
189 | user_supports() - provides information about what the user object supports |
190 | |
191 | =head3 STORE METHODS |
192 | |
193 | =over 4 |
194 | |
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195 | =item new( $config, $app, $realm ) |
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196 | |
197 | The C<new()> method is called only once, during the setup process of |
198 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication>. The |
199 | first argument, C<$config>, is a hash reference containing the configuration |
200 | information for the store module. The second argument is a reference to the |
201 | Catalyst application. |
202 | |
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203 | Note that when new() is called, Catalyst has not yet loaded |
204 | the various controller and model classes, nor is it definite |
205 | that other plugins have been loaded, so your new() method |
206 | must not rely on any of those being present. If any of |
207 | this is required for your store to function, you should |
208 | defer that part of initialization until the first method call. |
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209 | |
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210 | The C<new()> method should return a blessed reference to your store object. |
211 | |
212 | =item find_user( $authinfo, $c ) |
213 | |
214 | This is the workhorse of any authentication store. It's job is to take the |
215 | information provided to it via the C<$authinfo> hashref and locate the user |
216 | that matches it. It should return a reference to a user object. A return value |
217 | of anything else is considered to mean no user was found that matched the |
218 | information provided. |
219 | |
220 | How C<find_user()> accomplishes it's job is entirely up to you, the author, as |
221 | is what $authinfo is required to contain. Many stores will simply use a |
222 | username element in $authinfo to locate the user, but more advanced functionality |
223 | is possible and you may bend the $authinfo to your needs. Be aware, however, that |
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224 | both Credentials and Stores usually work with the same $authinfo hash, so take |
225 | care to avoid overlapping element names. |
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226 | |
227 | Please note that this routine may be called numerous times in various |
228 | circumstances, and that a successful match for a user here does B<NOT> |
229 | necessarily constitute successful authentication. Your store class should |
230 | never assume this and in most cases C<$c> B<should not be modified> by your |
231 | store object. |
232 | |
233 | =item for_session( $c, $user ) |
234 | |
235 | This method is responsible for preparing a user object for storage in the session. |
236 | It should return information that can be placed in the session and later used to |
237 | restore a user object (using the C<from_session()> method). It should therefore |
238 | ensure that whatever information provided can be used by the C<from_session()> |
239 | method to locate the unique user being saved. Note that there is no guarantee |
240 | that the same Catalyst instance will receive both the C<for_session()> and |
241 | C<from_session()> calls. You should take care to provide information that can |
242 | be used to restore a user, regardless of the current state of the application. |
243 | A good rule of thumb is that if C<from_session()> can revive the user with the |
244 | given information even if the Catalyst application has just started up, you are |
245 | in good shape. |
246 | |
247 | =item from_session( $c, $frozenuser ) |
248 | |
249 | This method is called whenever a user is being restored from the session. |
250 | C<$frozenuser> contains the information that was stored in the session for the user. |
251 | This will under normal circumstances be the exact data your store returned from |
252 | the previous call to C<for_session()>. C<from_session()> should return a valid |
253 | user object. |
254 | |
255 | =item user_supports( $feature, ... ) |
256 | |
257 | This method allows credentials and other objects to inquire as to what the |
258 | underlying user object is capable of. This is pretty-well free-form and the |
259 | main purpose is to allow graceful integration with credentials and |
260 | applications that may provide advanced functionality based on whether the |
261 | underlying user object can do certain things. In most cases you will want to |
262 | pass this directly to the underlying user class' C<supports> method. Note that |
263 | this is used as a B<class> method against the user class and therefore must |
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264 | be able to function without an instantiated user object. |
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265 | |
266 | =back |
267 | |
268 | =head2 USER OBJECT |
269 | |
270 | The user object is an important piece of your store module. It will be the |
271 | part of the system that the application developer will interact with most. As |
272 | such, the API for the user object is very rigid. All user objects B<MUST> |
273 | inherit from |
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274 | L<Catalyst::Authentication::User|Catalyst::Authentication::User>. |
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275 | |
276 | =head3 USER METHODS |
277 | |
278 | The routines required by the |
279 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> plugin |
280 | are below. Note that of these, only get_object is strictly required, as the |
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281 | L<Catalyst::Authentication::User|Catalyst::Authentication::User> |
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282 | base class contains reasonable implementations of the rest. If you do choose |
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283 | to implement only the C<get_object()> routine, please read the base class code |
284 | and documentation so that you fully understand how the other routines will be |
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285 | implemented for you. |
286 | |
287 | Also, your user object can implement whatever additional methods you require |
288 | to provide the functionality you need. So long as the below are implemented, |
289 | and you don't overlap the base class' methods with incompatible routines, you |
290 | should experience no problems. |
291 | |
292 | =over 4 |
293 | |
294 | =item id( ) |
295 | |
296 | The C<id()> method should return a unique id (scalar) that can be used to |
297 | retreive this user from the store. Often this will be provided to the store's |
298 | C<find_user()> routine as C<id =E<gt> $user-E<gt>id> so you should ensure that your |
299 | store's C<find_user()> can cope with that. |
300 | |
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301 | =item supports( $feature, $subfeature ... ) |
302 | |
303 | This method checks to see if the user class supports a particular feature. It |
304 | is implemented such that each argument provides a subfeature of the previous |
305 | argument. In other words, passing 'foo', 'bar' would return true if the user |
306 | supported the 'foo' feature, and the 'bar' feature of 'foo'. This is implemented |
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307 | in Catalyst::Authentication::User, so if your class inherits from that, you |
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308 | do not need to implement this and can instead implement supported_features(). |
309 | |
310 | B<Note:> If you want the authentication module to be able to save your user in |
311 | the session you must return true when presented with the feature 'session'. |
312 | |
313 | =item supported_features( ) |
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314 | |
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315 | This method should return a hashref of features supported by the user class. |
316 | This is for more flexible integration with some Credentials / applications. It |
317 | is not required that you support anything, and returning C<undef> is perfectly |
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318 | acceptable and in most cases what you will do. |
319 | |
320 | =item get( $fieldname ) |
321 | |
322 | This method should return the value of the field matching fieldname provided, |
323 | or undef if there is no field matching that fieldname. In most cases this will |
324 | access the underlying storage mechanism for the user data and return the |
325 | information. This is used as a standard method of accessing an authenticated |
326 | user's data, and MUST be implemented by all user objects. |
327 | |
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328 | B<Note>: There is no equivalent 'set' method. Each user class is |
329 | likely to vary greatly in how data must be saved and it is |
330 | therefore impractical to try to provide a standard way of |
331 | accomplishing it. When an application developer needs to save |
332 | data, they should obtain the underlying object / data by |
333 | calling get_object, and work with it directly. |
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334 | |
335 | |
336 | =item get_object( ) |
337 | |
338 | This method returns the underlying user object. If your user object is backed |
339 | by another object class, this method should return that underlying object. |
340 | This allows the application developer to obtain an editable object. Generally |
341 | speaking this will only be done by developers who know what they are doing and |
342 | require advanced functionality which is either unforeseen or inconsistent |
343 | across user classes. If your object is not backed by another class, or you |
344 | need to provide additional intermediate functionality, it is perfectly |
345 | reasonable to return C<$self>. |
346 | |
347 | =back |
348 | |
349 | |
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350 | =head1 WRITING A CREDENTIAL |
351 | |
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352 | Compared to writing a store, writing a credential is very simple. There is only |
353 | one class to implement, and it consists of only two required routines. They are: |
354 | |
355 | new() - instantiates the credential object |
356 | authenticate() - performs the authentication and returns a user object |
357 | |
358 | =head2 CREDENTIAL METHODS |
359 | |
360 | =over 4 |
361 | |
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362 | =item new( $config, $app, $realm ) |
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363 | |
364 | Like the Store method of the same name, the C<new()> method is called only |
365 | once, during the setup process of |
366 | L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication>. The |
367 | first argument, C<$config>, is a hash reference containing the configuration |
368 | information for the credential module. The second argument is a reference |
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369 | to the Catalyst application. $realm is the instantiated Realm object, which |
370 | you may use to access realm routines - such as find_user. |
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371 | |
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372 | Again, when the credential's new() method is called, Catalyst |
373 | has not yet loaded the various controller and model classes. |
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374 | |
375 | The new method should perform any necessary setup required and instantiate |
376 | your credential object. It should return your instantiated credential. |
377 | |
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378 | =item authenticate( $c, $realm, $authinfo ) |
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379 | |
380 | This is the workhorse of your credential. When $c->authenticate() is called |
381 | the L<Catalyst::Plugin::Authentication|Catalyst::Plugin::Authentication> module retrieves the |
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382 | realm object and passes it, along with the $authinfo hash |
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383 | to your credential's authenticate method. Your module should use the |
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384 | $authinfo hash to obtain the user from the realm passed, and then perform |
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385 | any credential verification steps necessary to authenticate the user. This |
386 | method should return the user object returned by the authentication store if |
387 | credential verification succeeded. It should return undef on failure. |
388 | |
389 | How your credential module performs the credential verification is entirely |
390 | up to you. In most cases, the credential will retrieve a user from the store |
391 | first (using the stores find_user() method), and then validate the user's |
392 | information. However, this does not have to be the case. |
393 | |
394 | It is perfectly acceptable for your credential to perform other tasks prior to |
395 | attempting to retrieve the user from the store. It may also make sense for |
396 | your credential to perform activities which help to locate the user in |
397 | question, for example, finding a user id based on an encrypted token. |
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398 | In these scenarios, the $authinfo hash passed to find_user() |
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399 | can be different than that which is passed in to $c->authenticate(). Once |
400 | again this is perfectly acceptable if it makes sense for your credential, |
401 | though you are strongly advised to note this behavior clearly in your |
402 | credential's documentation - as application authors are almost |
403 | certainly expecting the user to be found using the information provided |
404 | to $c->authenticate(). |
405 | |
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406 | Look at the L<Catalyst::Authentication::Credential::Password|Catalyst::Authentication::Credential::Password> |
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407 | module source to see this in action. In order to avoid possible |
408 | mismatches between the encrypted and unencrypted passwords, the password |
409 | credential actually removes the provided password from the authinfo |
410 | array. It does this because, in many cases, the store's password |
411 | field will be encrypted in some way, and the password passed to |
412 | $c->authenticate is almost certainly in plaintext. |
413 | |
414 | NOTE: You should always assume that a store is going to use all |
415 | the information passed to it to locate the user in question. |
416 | If there are fields in the $authinfo hash that you are sure |
417 | are specific to your credential, you may want to consider |
418 | removing them before user retrieval. A better solution is to |
419 | place those arguments that are specific to your credential |
420 | within their own subhash named after your module. |
421 | |
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422 | The L<Catalyst::Authentication::Store::DBIx::Class|Catalyst::Authentication::Store::DBIx::Class> module does this |
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423 | in order to encapsulate arguments intended specifically for |
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424 | that module. See the L<Catalyst::Authentication::Store::DBIx::Class::User|Catalyst::Authentication::Store::DBIx::Class::User> |
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425 | source for details. |
426 | |
427 | =back |
428 | |
429 | =head1 AUTHORS |
430 | |
431 | Jay Kuri, C<jayk@cpan.org> |
432 | |
433 | =head1 COPYRIGHT & LICENSE |
434 | |
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435 | Copyright (c) 2005 the aforementioned authors. All rights |
436 | reserved. This program is free software; you can redistribute |
437 | it and/or modify it under the same terms as Perl itself. |
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438 | |
439 | =cut |
440 | |
441 | |