squirrelmail/plugins/change_password/API

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    * Change Password plugin API *
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Document should explain how to create change_password plugin backends and 
provide details about plugin structure.

Plugin uses standard SquirrelMail plugin architecture and implements backends
with two hooks.

change_password_init hook
-------------------------
change_password_init hook is used to execute some code before displaying 
change password form. Plugin can use this hook to check if install has all 
required components, or to check if backend is configured correctly, or 
display some messages to end user. Maybe some background information about 
password security and how to choose good password. If backend detects some 
configuration errors that make backend unusable, it can stop execution of the 
script with PHP exit() call.

change_password_dochange hook
-----------------------------
change_password_dochange hook is used when user submits old and new passwords. 
Plugin checks if old password matches current session password and checks new 
password satisfies requirements set in plugin's configuration. All data is 
provided in array submitted via hook. 'username' key contains user's login 
name, 'curpw' contains current session password, 'newpw' contains new password.
Function that is attached to plugin should return empty array or array filled 
with error messages. If array is empty - plugin assumes that password was 
changed and updates current session password.

common strings
--------------
Backends can use constants for some error messages. CPW_CURRENT_NOMATCH 
constant sets 'Your current password is not correct.' error. CPW_INVALID_PW 
constant sets 'Your new password contains invalid characters.' error.

Recommendations
---------------
Backend should check, if current password matches stored password. 
Internal plugin functions only check if password matches the one that 
was used to login into SquirrelMail. Password is validated against IMAP 
server and not against used backend.

Backend should store only default configuration variables that don't 
have any information specific to developer's server or these variables
should be set to sane default values.

Backend's configuration should be controlled with configuration overrides
that are set config.php. It is recommended to use array with
configuration overrides and make sure that array is set to empty value 
before loading plugin's configuration file.

Backend should not use generic function names. It is recommended to use 
'cpw_' prefix.

If backend must load other SquirrelMail functions, it must use SM_PATH 
constant in include_once() calls and make sure that SM_PATH is defined
in any case when backend file is loaded. In most cases constant is 
already defined, but some unusual use of php files might cause php 
warnings, if constant is used inside backend functions and not defined 
in backend file.

Overrides used by backend and backend requirements must be documented 
in README file.