"""
This file contains (or should), all access control logic for the courseware.
Ideally, it will be the only place that needs to know about any special settings
like DISABLE_START_DATES.
Note: The access control logic in this file does NOT check for enrollment in
a course. It is expected that higher layers check for enrollment so we
don't have to hit the enrollments table on every module load.
If enrollment is to be checked, use get_course_with_access in courseware.courses.
It is a wrapper around has_access that additionally checks for enrollment.
"""
from datetime import datetime
import logging
import pytz
from django.conf import settings
from django.contrib.auth.models import AnonymousUser
from django.utils.timezone import UTC
from opaque_keys.edx.keys import CourseKey, UsageKey
from xblock.core import XBlock
from xmodule.course_module import (
CourseDescriptor,
CATALOG_VISIBILITY_CATALOG_AND_ABOUT,
CATALOG_VISIBILITY_ABOUT,
)
from xmodule.error_module import ErrorDescriptor
from xmodule.x_module import XModule
from xmodule.split_test_module import get_split_user_partitions
from xmodule.partitions.partitions import NoSuchUserPartitionError, NoSuchUserPartitionGroupError
from external_auth.models import ExternalAuthMap
from courseware.masquerade import get_masquerade_role, is_masquerading_as_student
from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
from student import auth
from student.models import CourseEnrollmentAllowed
from student.roles import (
CourseBetaTesterRole,
CourseCcxCoachRole,
CourseInstructorRole,
CourseStaffRole,
GlobalStaff,
SupportStaffRole,
OrgInstructorRole,
OrgStaffRole,
)
from util.milestones_helpers import (
get_pre_requisite_courses_not_completed,
any_unfulfilled_milestones,
is_prerequisite_courses_enabled,
)
from ccx_keys.locator import CCXLocator
from courseware.access_response import (
MilestoneError,
MobileAvailabilityError,
VisibilityError,
)
from courseware.access_utils import (
adjust_start_date, check_start_date, debug, ACCESS_GRANTED, ACCESS_DENIED,
in_preview_mode
)
from lms.djangoapps.ccx.custom_exception import CCXLocatorValidationException
from lms.djangoapps.ccx.models import CustomCourseForEdX
log = logging.getLogger(__name__)
def has_ccx_coach_role(user, course_key):
"""
Check if user is a coach on this ccx.
Arguments:
user (User): the user whose descriptor access we are checking.
course_key (CCXLocator): Key to CCX.
Returns:
bool: whether user is a coach on this ccx or not.
"""
if hasattr(course_key, 'ccx'):
ccx_id = course_key.ccx
role = CourseCcxCoachRole(course_key)
if role.has_user(user):
list_ccx = CustomCourseForEdX.objects.filter(
course_id=course_key.to_course_locator(),
coach=user
)
if list_ccx.exists():
coach_ccx = list_ccx[0]
return str(coach_ccx.id) == ccx_id
else:
raise CCXLocatorValidationException("Invalid CCX key. To verify that "
"user is a coach on CCX, you must provide key to CCX")
return False
def has_access(user, action, obj, course_key=None):
"""
Check whether a user has the access to do action on obj. Handles any magic
switching based on various settings.
Things this module understands:
- start dates for modules
- visible_to_staff_only for modules
- DISABLE_START_DATES
- different access for instructor, staff, course staff, and students.
- mobile_available flag for course modules
user: a Django user object. May be anonymous. If none is passed,
anonymous is assumed
obj: The object to check access for. A module, descriptor, location, or
certain special strings (e.g. 'global')
action: A string specifying the action that the client is trying to perform.
actions depend on the obj type, but include e.g. 'enroll' for courses. See the
type-specific functions below for the known actions for that type.
course_key: A course_key specifying which course run this access is for.
Required when accessing anything other than a CourseDescriptor, 'global',
or a location with category 'course'
Returns an AccessResponse object. It is up to the caller to actually
deny access in a way that makes sense in context.
"""
# Just in case user is passed in as None, make them anonymous
if not user:
user = AnonymousUser()
if in_preview_mode():
if not bool(has_staff_access_to_preview_mode(user=user, obj=obj, course_key=course_key)):
return ACCESS_DENIED
# delegate the work to type-specific functions.
# (start with more specific types, then get more general)
if isinstance(obj, CourseDescriptor):
return _has_access_course(user, action, obj)
if isinstance(obj, CourseOverview):
return _has_access_course(user, action, obj)
if isinstance(obj, ErrorDescriptor):
return _has_access_error_desc(user, action, obj, course_key)
if isinstance(obj, XModule):
return _has_access_xmodule(user, action, obj, course_key)
# NOTE: any descriptor access checkers need to go above this
if isinstance(obj, XBlock):
return _has_access_descriptor(user, action, obj, course_key)
if isinstance(obj, CCXLocator):
return _has_access_ccx_key(user, action, obj)
if isinstance(obj, CourseKey):
return _has_access_course_key(user, action, obj)
if isinstance(obj, UsageKey):
return _has_access_location(user, action, obj, course_key)
if isinstance(obj, basestring):
return _has_access_string(user, action, obj)
# Passing an unknown object here is a coding error, so rather than
# returning a default, complain.
raise TypeError("Unknown object type in has_access(): '{0}'"
.format(type(obj)))
# ================ Implementation helpers ================================
def has_staff_access_to_preview_mode(user, obj, course_key=None):
"""
Returns whether user has staff access to specified modules or not.
Arguments:
user: a Django user object.
obj: The object to check access for.
course_key: A course_key specifying which course this access is for.
Returns an AccessResponse object.
"""
if course_key is None:
if isinstance(obj, CourseDescriptor) or isinstance(obj, CourseOverview):
course_key = obj.id
elif isinstance(obj, ErrorDescriptor):
course_key = obj.location.course_key
elif isinstance(obj, XModule):
course_key = obj.descriptor.course_key
elif isinstance(obj, XBlock):
course_key = obj.location.course_key
elif isinstance(obj, CCXLocator):
course_key = obj.to_course_locator()
elif isinstance(obj, CourseKey):
course_key = obj
elif isinstance(obj, UsageKey):
course_key = obj.course_key
if course_key is None:
if GlobalStaff().has_user(user):
return ACCESS_GRANTED
else:
return ACCESS_DENIED
return _has_access_to_course(user, 'staff', course_key=course_key)
def _can_access_descriptor_with_start_date(user, descriptor, course_key): # pylint: disable=invalid-name
"""
Checks if a user has access to a descriptor based on its start date.
If there is no start date specified, grant access.
Else, check if we're past the start date.
Note:
We do NOT check whether the user is staff or if the descriptor
is detached... it is assumed both of these are checked by the caller.
Arguments:
user (User): the user whose descriptor access we are checking.
descriptor (AType): the descriptor for which we are checking access,
where AType is CourseDescriptor, CourseOverview, or any other class
that represents a descriptor and has the attributes .location, .id,
.start, and .days_early_for_beta.
Returns:
AccessResponse: The result of this access check. Possible results are
ACCESS_GRANTED or a StartDateError.
"""
return check_start_date(user, descriptor.days_early_for_beta, descriptor.start, course_key)
def _can_view_courseware_with_prerequisites(user, course): # pylint: disable=invalid-name
"""
Checks if a user has access to a course based on its prerequisites.
If the user is staff or anonymous, immediately grant access.
Else, return whether or not the prerequisite courses have been passed.
Arguments:
user (User): the user whose course access we are checking.
course (AType): the course for which we are checking access.
where AType is CourseDescriptor, CourseOverview, or any other
class that represents a course and has the attributes .location
and .id.
"""
def _is_prerequisites_disabled():
"""
Checks if prerequisites are disabled in the settings.
"""
return ACCESS_DENIED if is_prerequisite_courses_enabled() else ACCESS_GRANTED
return (
_is_prerequisites_disabled()
or _has_staff_access_to_descriptor(user, course, course.id)
or user.is_anonymous()
or _has_fulfilled_prerequisites(user, [course.id])
)
def _can_load_course_on_mobile(user, course):
"""
Checks if a user can view the given course on a mobile device.
This function only checks mobile-specific access restrictions. Other access
restrictions such as start date and the .visible_to_staff_only flag must
be checked by callers in *addition* to the return value of this function.
Arguments:
user (User): the user whose course access we are checking.
course (CourseDescriptor|CourseOverview): the course for which we are
checking access.
Returns:
bool: whether the course can be accessed on mobile.
"""
return (
is_mobile_available_for_user(user, course) and
(
_has_staff_access_to_descriptor(user, course, course.id) or
_has_fulfilled_all_milestones(user, course.id)
)
)
def _can_enroll_courselike(user, courselike):
"""
Ascertain if the user can enroll in the given courselike object.
Arguments:
user (User): The user attempting to enroll.
courselike (CourseDescriptor or CourseOverview): The object representing the
course in which the user is trying to enroll.
Returns:
AccessResponse, indicating whether the user can enroll.
"""
enrollment_domain = courselike.enrollment_domain
# Courselike objects (e.g., course descriptors and CourseOverviews) have an attribute named `id`
# which actually points to a CourseKey. Sigh.
course_key = courselike.id
# If using a registration method to restrict enrollment (e.g., Shibboleth)
if settings.FEATURES.get('RESTRICT_ENROLL_BY_REG_METHOD') and enrollment_domain:
if user is not None and user.is_authenticated() and \
ExternalAuthMap.objects.filter(user=user, external_domain=enrollment_domain):
debug("Allow: external_auth of " + enrollment_domain)
reg_method_ok = True
else:
reg_method_ok = False
else:
reg_method_ok = True
# If the user appears in CourseEnrollmentAllowed paired with the given course key,
# they may enroll. Note that as dictated by the legacy database schema, the filter
# call includes a `course_id` kwarg which requires a CourseKey.
if user is not None and user.is_authenticated():
if CourseEnrollmentAllowed.objects.filter(email=user.email, course_id=course_key):
return ACCESS_GRANTED
if _has_staff_access_to_descriptor(user, courselike, course_key):
return ACCESS_GRANTED
if courselike.invitation_only:
debug("Deny: invitation only")
return ACCESS_DENIED
now = datetime.now(UTC())
enrollment_start = courselike.enrollment_start or datetime.min.replace(tzinfo=pytz.UTC)
enrollment_end = courselike.enrollment_end or datetime.max.replace(tzinfo=pytz.UTC)
if reg_method_ok and enrollment_start < now < enrollment_end:
debug("Allow: in enrollment period")
return ACCESS_GRANTED
return ACCESS_DENIED
def _has_access_course(user, action, courselike):
"""
Check if user has access to a course.
Arguments:
user (User): the user whose course access we are checking.
action (string): The action that is being checked.
courselike (CourseDescriptor or CourseOverview): The object
representing the course that the user wants to access.
Valid actions:
'load' -- load the courseware, see inside the course
'load_forum' -- can load and contribute to the forums (one access level for now)
'load_mobile' -- can load from a mobile context
'enroll' -- enroll. Checks for enrollment window.
'see_exists' -- can see that the course exists.
'staff' -- staff access to course.
'see_in_catalog' -- user is able to see the course listed in the course catalog.
'see_about_page' -- user is able to see the course about page.
"""
def can_load():
"""
Can this user load this course?
NOTE: this is not checking whether user is actually enrolled in the course.
"""
response = (
_visible_to_nonstaff_users(courselike) and
_can_access_descriptor_with_start_date(user, courselike, courselike.id)
)
return (
ACCESS_GRANTED if (response or _has_staff_access_to_descriptor(user, courselike, courselike.id))
else response
)
def can_enroll():
"""
Returns whether the user can enroll in the course.
"""
return _can_enroll_courselike(user, courselike)
def see_exists():
"""
Can see if can enroll, but also if can load it: if user enrolled in a course and now
it's past the enrollment period, they should still see it.
"""
return ACCESS_GRANTED if (can_load() or can_enroll()) else ACCESS_DENIED
def can_see_in_catalog():
"""
Implements the "can see course in catalog" logic if a course should be visible in the main course catalog
In this case we use the catalog_visibility property on the course descriptor
but also allow course staff to see this.
"""
return (
_has_catalog_visibility(courselike, CATALOG_VISIBILITY_CATALOG_AND_ABOUT)
or _has_staff_access_to_descriptor(user, courselike, courselike.id)
)
def can_see_about_page():
"""
Implements the "can see course about page" logic if a course about page should be visible
In this case we use the catalog_visibility property on the course descriptor
but also allow course staff to see this.
"""
return (
_has_catalog_visibility(courselike, CATALOG_VISIBILITY_CATALOG_AND_ABOUT)
or _has_catalog_visibility(courselike, CATALOG_VISIBILITY_ABOUT)
or _has_staff_access_to_descriptor(user, courselike, courselike.id)
)
checkers = {
'load': can_load,
'view_courseware_with_prerequisites':
lambda: _can_view_courseware_with_prerequisites(user, courselike),
'load_mobile': lambda: can_load() and _can_load_course_on_mobile(user, courselike),
'enroll': can_enroll,
'see_exists': see_exists,
'staff': lambda: _has_staff_access_to_descriptor(user, courselike, courselike.id),
'instructor': lambda: _has_instructor_access_to_descriptor(user, courselike, courselike.id),
'see_in_catalog': can_see_in_catalog,
'see_about_page': can_see_about_page,
}
return _dispatch(checkers, action, user, courselike)
def _has_access_error_desc(user, action, descriptor, course_key):
"""
Only staff should see error descriptors.
Valid actions:
'load' -- load this descriptor, showing it to the user.
'staff' -- staff access to descriptor.
"""
def check_for_staff():
return _has_staff_access_to_descriptor(user, descriptor, course_key)
checkers = {
'load': check_for_staff,
'staff': check_for_staff,
'instructor': lambda: _has_instructor_access_to_descriptor(user, descriptor, course_key)
}
return _dispatch(checkers, action, user, descriptor)
def _has_group_access(descriptor, user, course_key):
"""
This function returns a boolean indicating whether or not `user` has
sufficient group memberships to "load" a block (the `descriptor`)
"""
if len(descriptor.user_partitions) == len(get_split_user_partitions(descriptor.user_partitions)):
# Short-circuit the process, since there are no defined user partitions that are not
# user_partitions used by the split_test module. The split_test module handles its own access
# via updating the children of the split_test module.
return ACCESS_GRANTED
# use merged_group_access which takes group access on the block's
# parents / ancestors into account
merged_access = descriptor.merged_group_access
# check for False in merged_access, which indicates that at least one
# partition's group list excludes all students.
if False in merged_access.values():
log.warning("Group access check excludes all students, access will be denied.", exc_info=True)
return ACCESS_DENIED
# resolve the partition IDs in group_access to actual
# partition objects, skipping those which contain empty group directives.
# If a referenced partition could not be found, it will be denied
# If the partition is found but is no longer active (meaning it's been disabled)
# then skip the access check for that partition.
partitions = []
for partition_id, group_ids in merged_access.items():
try:
partition = descriptor._get_user_partition(partition_id) # pylint: disable=protected-access
if partition.active:
if group_ids is not None:
partitions.append(partition)
else:
log.debug(
"Skipping partition with ID %s in course %s because it is no longer active",
partition.id, course_key
)
except NoSuchUserPartitionError:
log.warning("Error looking up user partition, access will be denied.", exc_info=True)
return ACCESS_DENIED
# next resolve the group IDs specified within each partition
partition_groups = []
try:
for partition in partitions:
groups = [
partition.get_group(group_id)
for group_id in merged_access[partition.id]
]
if groups:
partition_groups.append((partition, groups))
except NoSuchUserPartitionGroupError:
log.warning("Error looking up referenced user partition group, access will be denied.", exc_info=True)
return ACCESS_DENIED
# look up the user's group for each partition
user_groups = {}
for partition, groups in partition_groups:
user_groups[partition.id] = partition.scheme.get_group_for_user(
course_key,
user,
partition,
)
# finally: check that the user has a satisfactory group assignment
# for each partition.
if not all(user_groups.get(partition.id) in groups for partition, groups in partition_groups):
return ACCESS_DENIED
# all checks passed.
return ACCESS_GRANTED
def _has_access_descriptor(user, action, descriptor, course_key=None):
"""
Check if user has access to this descriptor.
Valid actions:
'load' -- load this descriptor, showing it to the user.
'staff' -- staff access to descriptor.
NOTE: This is the fallback logic for descriptors that don't have custom policy
(e.g. courses). If you call this method directly instead of going through
has_access(), it will not do the right thing.
"""
def can_load():
"""
NOTE: This does not check that the student is enrolled in the course
that contains this module. We may or may not want to allow non-enrolled
students to see modules. If not, views should check the course, so we
don't have to hit the enrollments table on every module load.
"""
response = (
_visible_to_nonstaff_users(descriptor)
and _has_group_access(descriptor, user, course_key)
and
(
_has_detached_class_tag(descriptor)
or _can_access_descriptor_with_start_date(user, descriptor, course_key)
)
)
return (
ACCESS_GRANTED if (response or _has_staff_access_to_descriptor(user, descriptor, course_key))
else response
)
checkers = {
'load': can_load,
'staff': lambda: _has_staff_access_to_descriptor(user, descriptor, course_key),
'instructor': lambda: _has_instructor_access_to_descriptor(user, descriptor, course_key)
}
return _dispatch(checkers, action, user, descriptor)
def _has_access_xmodule(user, action, xmodule, course_key):
"""
Check if user has access to this xmodule.
Valid actions:
- same as the valid actions for xmodule.descriptor
"""
# Delegate to the descriptor
return has_access(user, action, xmodule.descriptor, course_key)
def _has_access_location(user, action, location, course_key):
"""
Check if user has access to this location.
Valid actions:
'staff' : True if the user has staff access to this location
NOTE: if you add other actions, make sure that
has_access(user, location, action) == has_access(user, get_item(location), action)
"""
checkers = {
'staff': lambda: _has_staff_access_to_location(user, location, course_key)
}
return _dispatch(checkers, action, user, location)
def _has_access_course_key(user, action, course_key):
"""
Check if user has access to the course with this course_key
Valid actions:
'staff' : True if the user has staff access to this location
'instructor' : True if the user has staff access to this location
"""
checkers = {
'staff': lambda: _has_staff_access_to_location(user, None, course_key),
'instructor': lambda: _has_instructor_access_to_location(user, None, course_key),
}
return _dispatch(checkers, action, user, course_key)
def _has_access_ccx_key(user, action, ccx_key):
"""Check if user has access to the course for this ccx_key
Delegates checking to _has_access_course_key
Valid actions: same as for that function
"""
course_key = ccx_key.to_course_locator()
return _has_access_course_key(user, action, course_key)
def _has_access_string(user, action, perm):
"""
Check if user has certain special access, specified as string. Valid strings:
'global'
Valid actions:
'staff' -- global staff access.
'support' -- access to student support functionality
'certificates' --- access to view and regenerate certificates for other users.
"""
def check_staff():
"""
Checks for staff access
"""
if perm != 'global':
debug("Deny: invalid permission '%s'", perm)
return ACCESS_DENIED
return ACCESS_GRANTED if GlobalStaff().has_user(user) else ACCESS_DENIED
def check_support():
"""Check that the user has access to the support UI. """
if perm != 'global':
return ACCESS_DENIED
return (
ACCESS_GRANTED if GlobalStaff().has_user(user) or SupportStaffRole().has_user(user)
else ACCESS_DENIED
)
checkers = {
'staff': check_staff,
'support': check_support,
'certificates': check_support,
}
return _dispatch(checkers, action, user, perm)
##### Internal helper methods below
def _dispatch(table, action, user, obj):
"""
Helper: call table[action], raising a nice pretty error if there is no such key.
user and object passed in only for error messages and debugging
"""
if action in table:
result = table[action]()
debug("%s user %s, object %s, action %s",
'ALLOWED' if result else 'DENIED',
user,
obj.location.to_deprecated_string() if isinstance(obj, XBlock) else str(obj),
action)
return result
raise ValueError(u"Unknown action for object type '{0}': '{1}'".format(
type(obj), action))
def _adjust_start_date_for_beta_testers(user, descriptor, course_key): # pylint: disable=invalid-name
"""
If user is in a beta test group, adjust the start date by the appropriate number of
days.
Arguments:
user: A django user. May be anonymous.
descriptor: the XModuleDescriptor the user is trying to get access to, with a
non-None start date.
Returns:
A datetime. Either the same as start, or earlier for beta testers.
NOTE: number of days to adjust should be cached to avoid looking it up thousands of
times per query.
NOTE: For now, this function assumes that the descriptor's location is in the course
the user is looking at. Once we have proper usages and definitions per the XBlock
design, this should use the course the usage is in.
"""
return adjust_start_date(user, descriptor.days_early_for_beta, descriptor.start, course_key)
def _has_instructor_access_to_location(user, location, course_key=None):
if course_key is None:
course_key = location.course_key
return _has_access_to_course(user, 'instructor', course_key)
def _has_staff_access_to_location(user, location, course_key=None):
if course_key is None:
course_key = location.course_key
return _has_access_to_course(user, 'staff', course_key)
def _has_access_to_course(user, access_level, course_key):
"""
Returns True if the given user has access_level (= staff or
instructor) access to the course with the given course_key.
This ensures the user is authenticated and checks if global staff or has
staff / instructor access.
access_level = string, either "staff" or "instructor"
"""
if user is None or (not user.is_authenticated()):
debug("Deny: no user or anon user")
return ACCESS_DENIED
if not in_preview_mode() and is_masquerading_as_student(user, course_key):
return ACCESS_DENIED
if GlobalStaff().has_user(user):
debug("Allow: user.is_staff")
return ACCESS_GRANTED
if access_level not in ('staff', 'instructor'):
log.debug("Error in access._has_access_to_course access_level=%s unknown", access_level)
debug("Deny: unknown access level")
return ACCESS_DENIED
staff_access = (
CourseStaffRole(course_key).has_user(user) or
OrgStaffRole(course_key.org).has_user(user)
)
if staff_access and access_level == 'staff':
debug("Allow: user has course staff access")
return ACCESS_GRANTED
instructor_access = (
CourseInstructorRole(course_key).has_user(user) or
OrgInstructorRole(course_key.org).has_user(user)
)
if instructor_access and access_level in ('staff', 'instructor'):
debug("Allow: user has course instructor access")
return ACCESS_GRANTED
debug("Deny: user did not have correct access")
return ACCESS_DENIED
def _has_instructor_access_to_descriptor(user, descriptor, course_key): # pylint: disable=invalid-name
"""Helper method that checks whether the user has staff access to
the course of the location.
descriptor: something that has a location attribute
"""
return _has_instructor_access_to_location(user, descriptor.location, course_key)
def _has_staff_access_to_descriptor(user, descriptor, course_key):
"""Helper method that checks whether the user has staff access to
the course of the location.
descriptor: something that has a location attribute
"""
return _has_staff_access_to_location(user, descriptor.location, course_key)
def _visible_to_nonstaff_users(descriptor):
"""
Returns if the object is visible to nonstaff users.
Arguments:
descriptor: object to check
"""
return VisibilityError() if descriptor.visible_to_staff_only else ACCESS_GRANTED
def _has_detached_class_tag(descriptor):
"""
Returns if the given descriptor's type is marked as detached.
Arguments:
descriptor: object to check
"""
return ACCESS_GRANTED if 'detached' in descriptor._class_tags else ACCESS_DENIED # pylint: disable=protected-access
def _has_fulfilled_all_milestones(user, course_id):
"""
Returns whether the given user has fulfilled all milestones for the
given course.
Arguments:
course_id: ID of the course to check
user_id: ID of the user to check
"""
return MilestoneError() if any_unfulfilled_milestones(course_id, user.id) else ACCESS_GRANTED
def _has_fulfilled_prerequisites(user, course_id):
"""
Returns whether the given user has fulfilled all prerequisites for the
given course.
Arguments:
user: user to check
course_id: ID of the course to check
"""
return MilestoneError() if get_pre_requisite_courses_not_completed(user, course_id) else ACCESS_GRANTED
def _has_catalog_visibility(course, visibility_type):
"""
Returns whether the given course has the given visibility type
"""
return ACCESS_GRANTED if course.catalog_visibility == visibility_type else ACCESS_DENIED
def _is_descriptor_mobile_available(descriptor):
"""
Returns if descriptor is available on mobile.
"""
return ACCESS_GRANTED if descriptor.mobile_available else MobileAvailabilityError()
def is_mobile_available_for_user(user, descriptor):
"""
Returns whether the given course is mobile_available for the given user.
Checks:
mobile_available flag on the course
Beta User and staff access overrides the mobile_available flag
Arguments:
descriptor (CourseDescriptor|CourseOverview): course or overview of course in question
"""
return (
auth.user_has_role(user, CourseBetaTesterRole(descriptor.id))
or _has_staff_access_to_descriptor(user, descriptor, descriptor.id)
or _is_descriptor_mobile_available(descriptor)
)
def get_user_role(user, course_key):
"""
Return corresponding string if user has staff, instructor or student
course role in LMS.
"""
role = get_masquerade_role(user, course_key)
if role:
return role
elif has_access(user, 'instructor', course_key):
return 'instructor'
elif has_access(user, 'staff', course_key):
return 'staff'
else:
return 'student'