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Access API

The Access API gives you functions so you can determine what the current user is allowed to do. It also allows plugins to extend Moodle with new capabilities.

Overview

Moodle uses a role-based access control model. Entities are represented by contexts which are arranged into a tree-like hierarchy known as the context tree.

The following context types are available:

Context nameRepresentsImmediate contentsNotes
context_systemThe site as a wholeuser, course category, module, and blockThe System context is root context in the tree. There is only one System context
context_userAn individual userblockEach user has their own, unique, context
context_coursecatA single course categorycourse category, course, block
context_courseA single coursemodule, block
context_moduleAn activityblock
context_blockA blocknone

A Role is a set of capability definitions, where each capability represents something that the user is able to do. Roles are defined at the top most context in the context tree, the System context.

Roles can be overridden by contexts further down the tree.

User access is calculated from the combination of roles which are assigned to each user.

All users that did not log-in yet automatically get the default role defined in $CFG->notloggedinroleid, it is not possible to assign any other role to this non-existent user id. There is one special guest user account that is used when user logs in using the guest login button or when guest auto-login is enabled. Again you can not assign any roles to the guest account directly, this account gets the $CFG->guestroleid automatically. All other authenticated users get the default user role specified in $CFG->defaultuserroleid and in the frontpage context the role specified in $CFG->defaultfrontpageroleid.

Learn more on Moodle Academy
You can learn more about Contexts and the Roles API from the Moodle Access and Security Essentials on Moodle Academy.

How to define new capabilities in plugins

Capabilities are defined by $capabilities array defined in db/access.php files. The name of the capability consists of plugintype/pluginname:capabilityname.

For example:

mod/folder/db/access.php
$capabilities = [
'mod/folder:managefiles' => [
'riskbitmask' => RISK_SPAM,
'captype' => 'write',
'contextlevel' => CONTEXT_MODULE,
'archetypes' => [
'editingteacher' => CAP_ALLOW,
],
],
];

Where the meaning of array keys is:

FieldDescription
riskbitmaskassociated risks. These are explained on Hardening new Roles system.
captyperead or write capability type, for security reasons system prevents all write capabilities for guest account and not-logged-in users
contextlevelspecified as context level constant. Declares the typical context level where this capability is checked. This capability can be checked with contexts that are at a lower level (e.g. moodle/site:accessallgroups
archetypesspecifies defaults for roles with standard archetypes, this is used in installs, upgrades and when resetting roles (it is recommended to use only CAP_ALLOW here). Archetypes are defined in mdl_role table. See also Role archetypes.
clonepermissionsfromwhen you are adding a new capability, you can tell Moodle to copy the permissions for each role from the current settings for another capability. This may give better defaults than just using archetypes for administrators who have heavily customised their roles configuration. The full syntax is: clonepermissionsfrom => moodle/quiz:attempt

It is necessary to bump up plugin version number after any change in db/access.php, so that the upgrade scripts can make the necessary changes to the database. To run the upgrade scripts, log in to Moodle as administrator, navigate to the site home page, and follow the instructions. (If you need to test the upgrade script without changing the plugin version, it is also possible to set back the version number in the mdl_block or mdl_modules table in the database.)

The capability names are defined in plugin language files, the name of the string consists of "pluginname:capabilityname", in the example above it would be:

mod/folder/lang/en/folder.php
$string['folder:managefiles'] = 'Manage files in folder module';

Deprecating a capability

When a capability is no longer needed or is replaced by another, it should be deprecated. The timeline for deprecation should follow the normal Deprecation process.

To mark a capability as deprecated, edit the access.php containing the capability, remove it from the $capabilities array, and add it to the $deprecatedcapabilities array in this file.

Entries in $deprecatedcapabilities can have a replacement key indicating a new or existing capability that replaces the deprecated one. If this is specified, any checks to the deprecated capability will check the replacement capability instead. A debugging message will always be output at DEBUG_DEVELOPER level if a deprecated capability is checked.

$deprecatedcapaibilities can also define an optional message explaining the deprecation.

The following example demonstates an access.php file where a capability has been deprecated and replaced with another.

mod/folder/db/access.php
$capabilities = [
'mod/folder:newmanagefiles' => [
'riskbitmask' => RISK_SPAM,
'captype' => 'write',
'contextlevel' => CONTEXT_MODULE,
'archetypes' => [
'editingteacher' => CAP_ALLOW,
],
],
];

$deprecatedcapabilities = [
'mod/folder:managefiles' => [
'replacement' => 'mod/folder:newmanagefiles',
'message' => 'This was replaced with another capability'
],
];

Useful functions and classes

Context fetching

In plugins context instances are usually only instantiated because they are instantiated and deleted automatically by the system.

Fetching by object id:

$systemcontext = context_system::instance();
$usercontext = context_user::instance($user->id);
$categorycontext = context_coursecat::instance($category->id);
$coursecontext = context_course::instance($course->id);
$contextmodule = context_module::instance($cm->id);
$contextblock = context_block::instance($this->instance->id);

Fetching by context id:

$context = context::instance_by_id($contextid);

Notes:

  • by default exception is thrown if context can not be created
  • deleted users do not have contexts any more

Determining that a user has a given capability

When implementing access control always ask "Does the user have capability to do something?". It is incorrect to ask "Does the user have a role somewhere?".

has_capability()

has_capability() is the most important function:

function has_capability(
string $capability,
context $context,
object $user = null,
bool $doanything = true
): bool;

Check whether a user has a particular capability in a given context. For example:

$context = context_module::instance($cm->id);
if (has_capability('mod/folder:managefiles', $context)) {
// Do or display something.
}

By default checks the capabilities of the current user, but you can pass a different user id. By default will return true for admin users, it is not recommended to use false here.

require_capability()

Function require_capability() is very similar, it is throwing access control exception if user does not have the capability.

function require_capability($capability, context $context, $userid = null, $doanything = true, $errormessage = 'nopermissions', $stringfile = _) {

Enrolment functions

See Enrolment API.

function require_login($courseorid = null, $autologinguest = true, $cm = null, $setwantsurltome = true, $preventredirect = false)
function require_course_login($courseorid, $autologinguest = true, $cm = null, $setwantsurltome = true, $preventredirect = false)
function get_users_by_capability(context $context, $capability, $fields = _, $sort = _, $limitfrom = _, $limitnum = _,
$groups = _, $exceptions = _, $doanything_ignored = null, $view_ignored = null, $useviewallgroups = false)
function isguestuser($user = null)
function isloggedin()
function is_siteadmin($user_or_id = null)
function is_guest(context $context, $user = null)
function is_viewing(context $context, $user = null, $withcapability = _)

require_login()

Each plugin script should include require_login() or require_course_login() after setting up PAGE->url.

This function does following:

  • it verifies that user is logged in before accessing any course or activities (not-logged-in users can not enter any courses).
  • user is logged in as gu
  • verify access to hidden courses and activities
  • if an activity is specified, verify any availability restrictions for the activity
  • verify that user is either enrolled or has capability 'moodle/course:view' or some enrol plugin gives them temporary guest access
  • logs access to courses

require_course_login()

This function is supposed to be used only in activities that want to allow read access to content on the frontpage without logging-in. For example view resource files, reading of glossary entries, etc.

isguestuser(), isloggedin() and is_siteadmin()

These function were previously needed for limiting of access of special accounts. It is usually not necessary any more, because any write or risky capabilities are now automatically prevented in has_capability().

It is strongly discouraged to use is_siteadmin() in activity modules, please use standard capabilities and enrolment status instead.

is_guest(), is_viewing() and is_enrolled()

In order to access course data one of these functions must return true for user:

  • is_enrolled() - user has active record in user_enrolments table
  • is_viewing() - user has 'moodle/course:view' capability (may access course, but is not considered to be participant)
  • is_guest() - user was given temporary guest access by some enrolment plugin

get_users_by_capability()

This method returns list of users with given capability, it ignores enrolment status and should be used only above the course context.

See also