Roles API

The Roles API is an extension of the Access API and defines a set of actions that a user is allowed to perform on certain system levels. A capability defines a single permission (like posting to a forum) and a role is composed of a set of permissions, for example: a user with the Teacher role can add activities to a course, as well as managing course participants and grading course modules, while a user with a Non-editing Teacher role can only manage course participants and grade them, but not manage activities.

Definitions

• A role is an identifier of the user's status in some context. Teacher, Student and Forum moderator are all examples of possible roles.

• A capability is a description of some particular Moodle feature. Capabilities belong to a component. and are assigned to roles. For example, mod/forum:replypost is a capability.

• A permission is the level in which a capability is applied to a role. Example values include:

  • Allow
  • Prevent
  • Prohibit
  • Inherit

• A context is an area in Moodle. There are several context types for:

  • the whole site
  • a user
  • a course category
  • a course
  • an activity
  • a block

Roles

A role is defined with a list of permissions - each role definition is global defined and applies equally to all context levels, but these can be overridden in individual contexts. For example, a 'Student' role may not normally have the moodle/site:accessallgroups capability, but in the context of a specific forum the Teacher may grant this role. Permissions control possible user actions within Moodle (for example to delete discussions, add activities, and so on)

Roles can be applied to users in a context (for example to assign Fred as a Teacher in a particular course)

Context

Here are the possible contexts, listed from the most general to the most specific.

CONTEXT NAME	CONTEXT AREA	CONTEXT LEVEL
CONTEXT_SYSTEM	the whole site	10
CONTEXT_USER	another user	30
CONTEXT_COURSECAT	a course category	40
CONTEXT_COURSE	a course	50
CONTEXT_MODULE	an activity module	70
CONTEXT_BLOCK	a block	80

An authorized user will be able to assign an arbitrary number of roles to each user in any context.

See Roles and modules#Context for more information.

Capabilities

Capabilities can have the following permissions:

• CAP_INHERIT
• CAP_ALLOW
• CAP_PREVENT
• CAP_PROHIBIT

info

If no permission is defined for a capability in a role, then the permission is inherited from a context that is more general than the current context. If we define different permission values for the same capability in different contexts, we say that we are overriding the capability in the more specific context.

Capability conflicts

Since the capabilities in each role could be different, there can be conflicts in capabilities.

If we set a PROHIBIT on a capability, it means that the capability cannot be overridden and will ALWAYS have a permission of prevent (deny). Prohibit always wins. For example, Jeff has a naughty student role that prohibits him from postings in any forums (for the whole site), but he's also assigned a facilitator role in "Science forum" in the course Science and Math 101. Since prohibit always wins, Jeff is unable to post in "Science forum".

Another example would be, if a user has a Teacher and a Student role at the same time in a given course, then the following settings are possible:

• The moodle/site:accessallgroups capability is granted to the Teacher, but is prevented for the Student on site level
• The moodle/site:accessallgroups capability is granted to the Teacher, but is prevented for the Student in the category
• The moodle/site:accessallgroups capability is granted to the Teacher, but is prohibited for the Student in the category
• The moodle/site:accessallgroups capability is granted to the Teacher in the category, but is prevented for the Student in the course

Hardening Roles system

Hardening a role, refers to limiting the ability of a role to assign or to acquire permissions.

Roles have a great freedom when assigning capabilities to students. The problem might arise when students are assigned permission that allows adding of content that is not cleaned before display - such as editing resources or adding activities. They could then use any type of XSS attack to gain full administrative access quite easily.

The solution has two parts: educate admins and teachers about the risks associated with each capability and optionally allow central management of risks.

Risk bitmask in capabilities

Adds a risk bitmask field to each capability. Each bit indicates presence of different risk associated with given capability. Basic risks are

• RISK_SPAM - user can add a visible content to a site, send messages to other users
• RISK_PERSONAL - access to private personal information, for example backups with user details, non-public information in profile (hidden email)
• RISK_XSS - user can submit content that is not cleaned (both HTML with active content and unprotected files)
• RISK_CONFIG - user can change global configuration, actions are missing sanity checks
• RISK_MANAGETRUST - manage trust bitmasks of other users
• RISK_DATALOSS - can destroy large amounts of information that cannot easily be recovered. In default configuration Guest role should have only capabilities without risks, Student roles also SPAM, Teacher roles PERSONAL and XSS too. Admins have all capabilities by default.

When creating a new capability you might need to define risks and assign those in mod/xxx/db/access.php with riskbitmask:

$capabilities = [
    'tool/brickfield:viewcoursetools' => [
        'riskbitmask' => RISK_PERSONAL,
        'captype' => 'read',
        'contextlevel' => CONTEXT_COURSE,
        'archetypes' => [
            'teacher' => CAP_ALLOW,
            'editingteacher' => CAP_ALLOW,
            'manager' => CAP_ALLOW,
        ],
        'clonepermissionsfrom' => 'coursereport/participation:view',
    ],
];

Programming Interface

• Moodle comes with a list of predefined roles, including a Student, Teacher, Non-editing teacher, and Course Manager role. Each of these roles are based on a role archetype, which acts as a template for roles. Any custom role created by the site administrator can also choose to follow one of these role archetypes. When a plugin defines a new capability, it may specify how it would expect to be applied within these role archetypes, and these are applied to any role which follows this archetype. For example, if you create a new activity module with named mod_example, with a capability mod/example:view, you may specify that the teacher, and editingteacher archetypes are granted the capability with the allow permission. Any role which is based on these archetypes will be granted this capability with the 'allow' permission.

• The role archetypes do not change often, and are currently defined as:

  • manager - A system level role used to manage courses without being directly enrolled in them
  • coursecreator - A system level role used to create new courses
  • editingteacher - A course level role used to grade students as well as manage a given course
  • teacher - A course level role used to grade students (but not adding/editing activities)
  • student - A course level role for participating in a course, completing activities, but not grading other course participants
  • guest - Courses can allow non-authenticated access if desired. In general user with guest role not supposed to change anything like form submissions.
  • user - This role is assigned to every authenticated user.
  • frontpage - All authenticated users on site home page (which actually is a course).

Details

Fetching a list of the role archetypes programmatically

In some rare situations you may need to fetch a list of available role archetypes. You can do so using the get_role_archetypes() function, for example:

Fetching a list of role archetypes

$archetypes = get_role_archetypes();

• When handling a role on each page you need to find the context the user is working in, using the context::instance_by_id() or context_[type]::instance($typeid) function, for example:

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

Details

Fetching roles and users who hold a capability

Moodle has a flexible and detailed capability system which allows administrators to define many similar roles for different purposes. It is quite common to have multiple teacher-like roles but need to restrict their access depending on their usage. For example in a University setting you may have a lecturer who presents the course materials, and then a number of Ph.D students who lead smaller groups of students in labs, seminars, and workshops. These roles may both be considered a form of teacher, but they will have different permissions to suit their needs. As a result we strongly discourage that you think in terms of which roles or users hold a capability, but rather whether a specific user holds a capability.

There are some situations where you do need to get a list of roles with a capability in a specific

context, but these are very rare. You can do so using the get_roles_with_cap_in_context() function:

Fetching a list of roles which hold a capability in the specified context

[$roleids] = get_roles_with_cap_in_context($context, 'moodle/course:manageactivities');

Assigning user a role (for custom enrolment plugin development)

For certain institutions' enrolment process might be different to a standard workflow. For example enrolment is managed by an external system, so you might need to develop a custom Enrolment Plugin.

In case of custom enrolment plugin development only

To get a list of roles for a user

$ras = get_user_roles($context, $user, $checkparentcontexts);

To assign a role to a user

role_assign($roleid, $userid, $contextid, $component, $enrolmentpluginid);

See also

• Relevant discussions on moodle.org:
  • Roles and Capabilities forum