LTI Service - Platform

How to use the bundle to make your application act as a platform in the context of LTI services.

Providing platform service access token endpoint

The OAuth2AccessTokenCreationAction is automatically added to your application via the related flex recipe, in file config/routes/lti1p3.yaml.

Default route: [POST] '/lti1p3/auth/{keyChainIdentifier}/token'

This endpoint:

• allow tools to get granted to call your platform services endpoints, by following the client_credentials grant type with assertion.
• is working for a defined keyChainIdentifier as explained here, so you can expose several of them if your application is acting as several deployed platforms
• is able to grant (give access tokens) for a defined list of allowed scopes

You must first configure the list of allowed scopes to grant access tokens:

# config/packages/lti1p3.yaml
lti1p3:
    scopes:
        - 'https://purl.imsglobal.org/spec/lti-ags/scope/lineitem'
        - 'https://purl.imsglobal.org/spec/lti-ags/scope/result/read'

Then, if you configure a key chain as following:

# config/packages/lti1p3.yaml
lti1p3:
    key_chains:
        platformKey:
            key_set_name: "platformSet"
            public_key: "file://path/to/public.key"
            private_key: "file://path/to/private.key"
            private_key_passphrase: 'someSecretPassPhrase'

You can then configure a platform as following (using the key chain identifier platformKey):

# config/packages/lti1p3.yaml
lti1p3:
    platforms:
        myPlatform:
            name: "My Platform"
            audience: "http://platform.com"
            oidc_authentication_url: "http://platform.com/lti1p3/oidc/authentication"
            oauth2_access_token_url: "http://platform.com/lti1p3/auth/platformKey/token"

Once set up, tools can request access tokens by following the client_credentials grant type with assertion:

• grant_type: client_credentials
• client_assertion_type: urn:ietf:params:oauth:client-assertion-type:jwt-bearer
• client_assertion: the tool's generated JWT assertion
• scope: https://purl.imsglobal.org/spec/lti-ags/scope/lineitem https://purl.imsglobal.org/spec/lti-ags/scope/result/read

Request example:

POST /lti1p3/auth/platformKey/token HTTP/1.1
Host: example.com
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials
&client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJ0eXAiOi....
&scope=http%3A%2F%2Fimsglobal.org%2Fspec%2Flti-ags%2Fscope%2Flineitem%20http%3A%2F%2Fimsglobal.org%2Fspec%2Flti-ags%2Fscope%2Fresult%2Fread 

As a response, the OAuth2AccessTokenCreationAction will offer an access token (following OAuth2 standards), valid for 3600 seconds:

HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache

{
    "access_token" : "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1N.....",
    "token_type" : "bearer",
    "expires_in" : 3600,
    "scope" : "https://purl.imsglobal.org/spec/lti-ags/scope/lineitem https://purl.imsglobal.org/spec/lti-ags/scope/result/read"    
} 

Notes:

• a HTTP 400 response is returned if the requested scopes are not configured, or invalid
• a HTTP 401 response is returned if the client assertion cannot match a registered tool
• to automate (and cache) authentication grants from the tools side, a LtiServiceClient is ready to use for your LTI service calls as explained here

Protecting platform service endpoints

For example, considering you have the following platform service endpoints:

#config/routes.yaml
platform_service_ags_lineitem:
    path: /platform/service/ags/lineitem
    controller: App\Action\Platform\Service\Ags\LineItemAction
platform_service_ags_result:
    path: /platform/service/ags/result
    controller: App\Action\Platform\Service\Ags\ResultAction

To protect your endpoint, this bundle provides the lti1p3_service security firewall to put in front of your routes:

# config/packages/security.yaml
security:
    firewalls:
        secured_service_ags_lineitem_area:
            pattern: ^/platform/service/ags/lineitem
            stateless: true
            lti1p3_service: { scopes: ['https://purl.imsglobal.org/spec/lti-ags/scope/lineitem'] }
        secured_service_ags_result_area:
            pattern: ^/platform/service/ags/result
            stateless: true
            lti1p3_service: { scopes: ['https://purl.imsglobal.org/spec/lti-ags/scope/result/read'] }

Note: you can define per firewall the list of allowed scopes, to have better granularity for your endpoints protection.

It will:

• handle the provided access token validation (signature validity, expiry, matching configured firewall scopes, etc ...)
• add on success a LtiServiceSecurityToken in the security token storage, that you can use to retrieve your authentication context

For example (in one of the endpoints):

<?php

declare(strict_types=1);

namespace App\Action\Platform\Service\Ags;

use OAT\Bundle\Lti1p3Bundle\Security\Authentication\Token\Service\LtiServiceSecurityToken;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Security\Core\Security;

class LineItemAction
{
    /** @var Security */
    private $security;

    public function __construct(Security $security)
    {
        $this->security = $security;
    }

    public function __invoke(Request $request): Response
    {
        /** @var LtiServiceSecurityToken $token */
        $token = $this->security->getToken();

        // Related registration (to spare queries)
        $registration = $token->getRegistration();

        // Related access token
        $token = $token->getAccessToken();

        // Related scopes (if you want to implement some ACL)
        $scopes = $token->getScopes(); // ['https://purl.imsglobal.org/spec/lti-ags/scope/lineitem']

        // You can even access validation results
        $validationResults = $token->getValidationResult();

        // Your service endpoint logic ...

        return new Response(...);
    }
}

Providing platform service endpoints using the LTI libraries

We provide a collection of LTI libraries to offer LTI capabilities (NRPS, AGS, basic outcomes, etc) to your application.

The bundle provides a way to easily integrate them when it comes to expose LTI services endpoints:

• the core LtiServiceServerRequestHandlerInterface is implemented by those libraries to provide their service endpoints logic
• the bundle LtiServiceServerHttpFoundationRequestHandlerInterface symfony service automates any LtiServiceServerRequestHandlerInterface implementation execution
• the bundle LtiServiceServerHttpFoundationRequestHandlerFactoryInterface symfony service can be used to ease the LtiServiceServerHttpFoundationRequestHandlerInterface creation (symfony service factory)

For example, let's implement step by step the NRPS library membership service endpoint into your application:

• install the library

$ composer require oat-sa/lib-lti1p3-nrps

• allow NRPS scope

# config/packages/lti1p3.yaml
lti1p3:
    scopes:
        - 'https://purl.imsglobal.org/spec/lti-nrps/scope/contextmembership.readonly'

• provide a required MembershipServiceServerBuilderInterface implementation

<?php

declare(strict_types=1);

namespace App\Nrps;

use OAT\Library\Lti1p3Core\Registration\RegistrationInterface;
use OAT\Library\Lti1p3Nrps\Model\Membership\MembershipInterface;
use OAT\Library\Lti1p3Nrps\Service\Server\Builder\MembershipServiceServerBuilderInterface;

class MembershipServiceServerBuilder implements MembershipServiceServerBuilderInterface 
{
    public function buildContextMembership(
        RegistrationInterface $registration,
        ?string $role = null,
        ?int $limit = null,
        ?int $offset = null
    ): MembershipInterface {
        // Logic for building context membership for a given registration
    }

    public function buildResourceLinkMembership(
        RegistrationInterface $registration,
        string $resourceLinkIdentifier,
        ?string $role = null,
        ?int $limit = null,
        ?int $offset = null
    ): MembershipInterface {
        // Logic for building resource link membership for a given registration and resource link identifier
    }
};

• register the NRPS library request handler using your builder in your application services

# config/services.yaml
services:
    OAT\Library\Lti1p3Nrps\Service\Server\Handler\MembershipServiceServerRequestHandler:
        arguments:
            - '@App\Nrps\MembershipServiceServerBuilder'

• use the LtiServiceServerHttpFoundationRequestHandlerFactoryInterface service factory to create a controller service

# config/services.yaml
services:
    app.nrps_membership_controller:
        class: OAT\Bundle\Lti1p3Bundle\Service\Server\Handler\LtiServiceServerHttpFoundationRequestHandler
        factory: ['@OAT\Bundle\Lti1p3Bundle\Service\Server\Factory\LtiServiceServerHttpFoundationRequestHandlerFactoryInterface', 'create']
        arguments:
            - '@OAT\Library\Lti1p3Nrps\Service\Server\Handler\MembershipServiceServerRequestHandler'
        tags: ['controller.service_arguments']

• bind this controller service to a route in your application

# config/routes.yaml
nrps_membership:
    path: /platform/service/nrps
    controller: app.nrps_membership_controller

• protect this route using the bundle service firewall

# config/packages/security.yaml
security:
    firewalls:
        secured_service_nrps_area:
            pattern: ^/platform/service/nrps
            stateless: true
            lti1p3_service: { scopes: ['https://purl.imsglobal.org/spec/lti-nrps/scope/contextmembership.readonly'] }

At this point, your application now offers a new endpoint [GET] /platform/service/nrps, that automates:

• HTTP method validation
• NRPS content type validation
• access token validation
• access token NRPS scope validation
• the response of NRPS memberships representations, relying on the provided membership builder implementation

Note: exposing a controller as service is convenient but not mandatory, you can still inject the LtiServiceServerHttpFoundationRequestHandlerFactoryInterface in a controller constructor to have more control on this process, as done in the bundle TestServiceAction for example.