PyLTI1p3 1.8.6

LTI 1.3 Advantage Tool implementation in Python

LTI 1.3 Advantage Tool implementation in Python
===============================================

.. image:: https://img.shields.io/pypi/v/PyLTI1p3
:scale: 100%
:target: https://pypi.python.org/pypi/PyLTI1p3
:alt: PyPI

.. image:: https://img.shields.io/pypi/pyversions/PyLTI1p3
:scale: 100%
:target: https://www.python.org/
:alt: Python

.. image:: https://travis-ci.com/dmitry-viskov/pylti1.3.svg?branch=master
:scale: 100%
:target: https://travis-ci.com/dmitry-viskov/pylti1.3
:alt: Build Status

.. image:: https://img.shields.io/github/license/dmitry-viskov/pylti1.3
:scale: 100%
:target: https://raw.githubusercontent.com/dmitry-viskov/pylti1.3/master/LICENSE
:alt: MIT


This project is a Python implementation of the similar `PHP tool`_.
This library contains adapters for use with the Django and Flask web frameworks. However, there are no difficulties with adapting it to other frameworks; you just need to re-implement the ``OIDCLogin`` and ``MessageLaunch`` classes as it is already done in existing adapters.

.. _PHP tool: https://github.com/IMSGlobal/lti-1-3-php-library

Usage Examples
=================

Django: https://github.com/dmitry-viskov/pylti1.3-django-example

Flask: https://github.com/dmitry-viskov/pylti1.3-flask-example

Configuration
=============

To configure your own tool, you may use built-in adapters:

.. code-block:: python

from pylti1p3.tool_config import ToolConfJsonFile
tool_conf = ToolConfJsonFile('path/to/json')

from pylti1p3.tool_config import ToolConfDict
settings = {
"<issuer_1>": { }, # one issuer ~ one client-id (outdated and not recommended)
"<issuer_2>": [{ }, { }] # one issuer ~ many client-ids (recommended method)
}
private_key = '...'
public_key = '...'
tool_conf = ToolConfDict(settings)

client_id = '...' # must be set if implementing the "one issuer ~ many client-ids" concept

tool_conf.set_private_key(iss, private_key, client_id=client_id)
tool_conf.set_public_key(iss, public_key, client_id=client_id)

or create your own implementation. The ``pylti1p3.tool_config.ToolConfAbstract`` interface must be fully implemented for this to work.
The concept of ``one issuer ~ many client-ids`` is the recommended way to organize configs and may be useful in the case of integration with Canvas (https://canvas.instructure.com)
or other Cloud LMS-es where the platform doesn't change ``iss`` for each customer.

In the case of the Django Framework, you may use ``DjangoDbToolConf`` (see `Configuration using Django Admin UI`_ section below).


Example of a JSON config:

.. code-block:: javascript

{
"iss1": [{
"default": true,
"client_id": "client_id1",
"auth_login_url": "auth_login_url1",
"auth_token_url": "auth_token_url1",
"auth_audience": null,
"key_set_url": "key_set_url1",
"key_set": null,
"private_key_file": "private.key",
"public_key_file": "public.key",
"deployment_ids": ["deployment_id1", "deployment_id2"]
}, {
"default": false,
"client_id": "client_id2",
"auth_login_url": "auth_login_url2",
"auth_token_url": "auth_token_url2",
"auth_audience": null,
"key_set_url": "key_set_url2",
"key_set": null,
"private_key_file": "private.key",
"public_key_file": "public.key",
"deployment_ids": ["deployment_id3", "deployment_id4"]
}],
"iss2": [ ],
"iss3": { }
}


| ``default (bool)`` - this iss config will be used in case if client-id was not passed on the login step
| ``client_id`` - this is the id received in the 'aud' during a launch
| ``auth_login_url`` - the platform's OIDC login endpoint
| ``auth_token_url`` - the platform's service authorization endpoint
| ``auth_audience`` - the platform's OAuth2 Audience (aud). Is used to get platform's access token. Usually the same as "auth_token_url" and could be skipped but in the common case could be a different url
| ``key_set_url`` - the platform's JWKS endpoint
| ``key_set`` - in case if platform's JWKS endpoint somehow unavailable you may paste JWKS here
| ``private_key_file`` - relative path to the tool's private key
| ``public_key_file`` - relative path to the tool's public key
| ``deployment_ids (list)`` - The deployment_id passed by the platform during launch

Usage with Django
=================

.. _Configuration:

Configuration using Django Admin UI
-----------------------------------

.. code-block:: python

# settings.py

INSTALLED_APPS = [
'django.contrib.admin',
...
'pylti1p3.contrib.django.lti1p3_tool_config'
]

# urls.py

urlpatterns = [
...
path('admin/', admin.site.urls),
...
]

# views.py

from pylti1p3.contrib.django import DjangoDbToolConf

tool_conf = DjangoDbToolConf()


Open Id Connect Login Request
-----------------------------

LTI 1.3 uses a modified version of the OpenId Connect third party initiate login flow. This means that to do an LTI 1.3 launch, you must first receive a login initialization request and return to the platform.

To handle this request, you must first create a new ``OIDCLogin`` (or ``DjangoOIDCLogin``) object:

.. code-block:: python

from pylti1p3.contrib.django import DjangoOIDCLogin

oidc_login = DjangoOIDCLogin(request, tool_conf)

You must now configure your login request with a return url (this must be preconfigured and white-listed in the tool).
If a redirect url is not given or the registration does not exist, a ``pylti1p3.exception.OIDC_Exception`` will be thrown.

.. code-block:: python

try:
oidc_login.redirect(get_launch_url(request))
except OIDC_Exception:
# display error page
log.error('Error doing OIDC login')

With the redirect, we can now redirect the user back to the tool.
There are three ways to do this:

This will add a HTTP 302 location header:

.. code-block:: python

oidc_login.redirect(get_launch_url(request))

This will display some JavaScript to do the redirect instead of using a HTTP 302:

.. code-block:: python

oidc_login.redirect(get_launch_url(request), js_redirect=True)

You can also get the url you need to redirect to, with all of the necessary query parameters (if you would prefer to redirect in a custom way):

.. code-block:: python

redirect_obj = oidc_login.get_redirect_object()
redirect_url = redirect_obj.get_redirect_url()

The redirect is done and we can move on to the launch.

LTI Message Launches
--------------------

Now that we have done the OIDC log, the platform will launch back to the tool. To handle this request, we first need to create a new ``MessageLaunch`` (or ``DjangoMessageLaunch``) object.

.. code-block:: python

message_launch = DjangoMessageLaunch(request, tool_conf)

Once we have the message launch, we can validate it. Validation is transparent - it's done once before you try to access the message body:

.. code-block:: python

try:
launch_data = message_launch.get_launch_data()
except LtiException:
log.error('Launch validation failed')

You may do it more explicitly:

.. code-block:: python

try:
launch_data = message_launch.set_auto_validation(enable=False).validate()
except LtiException:
log.error('Launch validation failed')

Now that we know the launch is valid, we can find out more information about the launch.

To check if we have a resource launch or a deep linking launch:

.. code-block:: python

if message_launch.is_resource_launch():
# Resource Launch!
elif message_launch.is_deep_link_launch():
# Deep Linking Launch!
else:
# Unknown launch type

To check which services we have access to:

.. code-block:: python

if message_launch.has_ags():
# Has Assignments and Grades Service
if message_launch.has_nrps():
# Has Names and Roles Service

Accessing Cached Launch Requests
--------------------------------

It is likely that you will want to refer back to a launch later during subsequent requests. This is done using the launch id to identify a cached request. The launch id can be found using:

.. code-block:: python

launch_id = message_launch.get_launch_id()

Once you have the launch id, you can link it to your session and pass it along as a query parameter.

Retrieving a launch using the launch id can be done using:

.. code-block:: python

message_launch = DjangoMessageLaunch.from_cache(launch_id, request, tool_conf)

Once retrieved, you can call any of the methods on the launch object as normal, e.g.

.. code-block:: python

if message_launch.has_ags():
# Has Assignments and Grades Service

Deep Linking Responses
----------------------

If you receive a deep linking launch, it is very likely that you are going to want to respond to the deep linking request with resources for the platform.

To create a deep link response, you will need to get the deep link for the current launch:

.. code-block:: python

deep_link = message_launch.get_deep_link()

We now need to create ``pylti1p3.deep_link_resource.DeepLinkResource`` to return:

.. code-block:: python

resource = DeepLinkResource()
resource.set_url("https://my.tool/launch")\
.set_custom_params({'my_param': my_param})\
.set_title('My Resource')

Everything is now set to return the resource to the platform. There are two methods of doing this.

The following method will output the html for an aut-posting form for you.

.. code-block:: python

deep_link.output_response_form([resource1, resource2])

Alternatively you can just request the signed JWT that will need posting back to the platform by calling.

.. code-block:: python

deep_link.get_response_jwt([resource1, resource2])

Names and Roles Service
-----------------------

Before using names and roles, you should check that you have access to it:

.. code-block:: python

if not message_launch.has_nrps():
raise Exception("Don't have names and roles!")

Once we know we can access it, we can get an instance of the service from the launch.

.. code-block:: python

nrps = message_launch.get_nrps()

From the service we can get a list of all members by calling:

.. code-block:: python

members = nrps.get_members()

Assignments and Grades Service
------------------------------

Before using assignments and grades, you should check that you have access to it:

.. code-block:: python

if not launch.has_ags():
raise Exception("Don't have assignments and grades!")

Once we know we can access it, we can get an instance of the service from the launch:

.. code-block:: python

ags = launch.get_ags()

To pass a grade back to the platform, you will need to create a ``pylti1p3.grade.Grade`` object and populate it with the necessary information:

.. code-block:: python

gr = Grade()
gr.set_score_given(earned_score)\
.set_score_maximum(100)\
.set_timestamp(datetime.datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%S+0000'))\
.set_activity_progress('Completed')\
.set_grading_progress('FullyGraded')\
.set_user_id(external_user_id)

To send the grade to the platform we can call:

.. code-block:: python

ags.put_grade(gr)

This will put the grade into the default provided lineitem. If no default lineitem exists it will create one.

If you want to send multiple types of grade back, that can be done by specifying a ``pylti1p3.lineitem.LineItem``:

.. code-block:: python

line_item = LineItem()
line_item.set_tag('grade')\
.set_score_maximum(100)\
.set_label('Grade')

ags.put_grade(gr, line_item)

If a lineitem with the same ``tag`` exists, that lineitem will be used, otherwise a new lineitem will be created.

Check user's role after LTI launch
----------------------------------

.. code-block:: python

user_is_staff = message_launch.check_staff_access()
user_is_student = message_launch.check_student_access())
user_is_teacher = message_launch.check_teacher_access()
user_is_teaching_assistant = message_launch.check_teaching_assistant_access()
user_is_designer = message_launch.check_designer_access()
user_is_observer = message_launch.check_observer_access()
user_is_transient = message_launch.check_transient()

Usage with Flask
================

Open Id Connect Login Request
-----------------------------

This is a draft of an API endpoint. Wrap it in a library of your choice.

Create a ``FlaskRequest`` adapter. Then create an instance of ``FlaskOIDCLogin``. The ``redirect`` method will return an instance of ``werkzeug.wrappers.Response`` that points to the LTI platform if login was successful. Make sure to handle exceptions.

.. code-block:: python

from flask import request, session
from pylti1p3.flask_adapter import (FlaskRequest, FlaskOIDCLogin)

def login(request_params_dict):

tool_conf = ... # See Configuration chapter above

# FlaskRequest by default use flask.request and flask.session
# so in this case you may define request object without any arguments:

request = FlaskRequest()

# in case of using different request object (for example webargs or something like this)
# you may pass your own values:

request = FlaskRequest(
cookies=request.cookies,
session=session,
request_data=request_params_dict,
request_is_secure=request.is_secure
)

oidc_login = FlaskOIDCLogin(
request=request,
tool_config=tool_conf,
session_service=FlaskSessionService(request),
cookie_service=FlaskCookieService(request)
)

return oidc_login.redirect(request.get_param('target_link_uri'))

LTI Message Launches
--------------------

This is a draft of an API endpoint. Wrap it in a library of your choice.

Create a ``FlaskRequest`` adapter. Then create an instance of ``FlaskMessageLaunch``. This lets you access data from the LTI launch message if the launch was successful. Make sure to handle exceptions.

.. code-block:: python

from flask import request, session
from werkzeug.utils import redirect
from pylti1p3.flask_adapter import (FlaskRequest, FlaskMessageLaunch)

def launch(request_params_dict):

tool_conf = ... # See Configuration chapter above

request = FlaskRequest()

# or

request = FlaskRequest(
cookies=...,
session=...,
request_data=...,
request_is_secure=...
)

message_launch = FlaskMessageLaunch(
request=request,
tool_config=tool_conf
)

email = message_launch.get_launch_data().get('email')

# Place your user creation/update/login logic
# and redirect to tool content here

Cookies issues in the iframes
=============================

Some browsers may deny requests to save cookies in the iframes. For example, `Google Chrome (from ver.80 onwards) denies requests to save`_ all cookies in
the iframes except cookies with the flags ``Secure`` (i.e HTTPS usage) and ``SameSite=None``. `Safari denies requests to save`_
all third-party cookies by default. The ``pylti1p3`` library contains workarounds for such behaviours:

.. _Google Chrome (from ver.80 onwards) denies requests to save: https://blog.heroku.com/chrome-changes-samesite-cookie
.. _Safari denies requests to save: https://webkit.org/blog/10218/full-third-party-cookie-blocking-and-more/

.. code-block:: python

def login():
...
return oidc_login\
.enable_check_cookies()\
.redirect(target_link_uri)

After this, the special JS code will try to write and then read test cookie instead of redirect. The user will see a
`special page`_ that will ask them to open the current URL in the new window if cookies are unavailable. If
cookies are allowed, the user will be transparently redirected to the next page. All texts are configurable with passing arguments:

.. _special page: https://raw.githubusercontent.com/dmitry-viskov/repos-assets/master/pylti1p3/examples/cookies-check/001.png

.. code-block:: python

oidc_login.enable_check_cookies(main_msg, click_msg, loading_msg)

You may also have troubles with the default framework sessions because the ``pylti1p3`` library can't control your framework
settings connected with the session ID cookie. Without necessary settings, the user's session could be unavailable in the
case of iframe usage. To avoid this, it is recommended to change the default session adapter to the new cache
adapter (with a memcache/redis backend) andl as a consequence, allow the library to set its own LTI 1.3 session id cookie
that will be set with all necessary params like `Secure` and `SameSite=None`.

Django cache data storage
-------------------------

.. code-block:: python

from pylti1p3.contrib.django import DjangoCacheDataStorage

def login(request):
...
launch_data_storage = DjangoCacheDataStorage(cache_name='default')
oidc_login = DjangoOIDCLogin(request, tool_conf, launch_data_storage=launch_data_storage)

def launch(request):
...
launch_data_storage = DjangoCacheDataStorage(cache_name='default')
message_launch = DjangoMessageLaunch(request, tool_conf, launch_data_storage=launch_data_storage)

def restore_launch(request):
...
launch_data_storage = get_launch_data_storage(cache_name='default')
message_launch = DjangoMessageLaunch.from_cache(launch_id, request, tool_conf,
launch_data_storage=launch_data_storage)

Flask cache data storage
-------------------------

.. code-block:: python

from flask_caching import Cache
from pylti1p3.contrib.flask import FlaskCacheDataStorage

cache = Cache(app)

def login():
...
launch_data_storage = FlaskCacheDataStorage(cache)
oidc_login = DjangoOIDCLogin(request, tool_conf, launch_data_storage=launch_data_storage)

def launch():
...
launch_data_storage = FlaskCacheDataStorage(cache)
message_launch = DjangoMessageLaunch(request, tool_conf, launch_data_storage=launch_data_storage)

def restore_launch():
...
launch_data_storage = FlaskCacheDataStorage(cache)
message_launch = DjangoMessageLaunch.from_cache(launch_id, request, tool_conf,
launch_data_storage=launch_data_storage)

Cache for Public Key
====================

The library will try to fetch the platform's public key every time on the message launch step. This public key may be stored in cache
(memcache/redis) to speed-up the launch process:

.. code-block:: python

# Django cache storage:
launch_data_storage = DjangoCacheDataStorage()

# Flask cache storage:
launch_data_storage = FlaskCacheDataStorage(cache)

message_launch.set_public_key_caching(launch_data_storage, cache_lifetime=7200)


API to get JWKS
===============

You may generate JWKS from a Tool Config object:

.. code-block:: python

tool_conf.set_public_key(iss, public_key, client_id=client_id)
jwks_dict = tool_conf.get_jwks() # {"keys": [{ ... }]}

# or you may specify iss and client_id:
jwks_dict = tool_conf.get_jwks(iss, client_id) # {"keys": [{ ... }]}

Do not forget to set a public key as without it, JWKS cannot be generated.
You may also generate JWK for any public key using the construction below:

.. code-block:: python

from pylti1p3.registration import Registration

jwk_dict = Registration.get_jwk(public_key)
# {"e": ..., "kid": ..., "kty": ..., "n": ..., "alg": ..., "use": ...}