NP.Lti13Platform.Core 1.0.0-preview003

NP.Lti13Platform.Core

The IMS Lti Core spec defines a way that platforms can launch resources that exist in the tool. This project provides an implementation of the spec.

Features

• Launch the links to the tool
• Handle authentication with the tool
• Create tokens for services

Getting Started

1. Add the nuget package to your project:

2. Add an implementation of the ILti13CoreDataService interface:

public class DataService: ILti13CoreDataService
{
    ...
}

3. Add the required services.

builder.Services
    .AddLti13PlatformCore()
    .WithLti13CoreDataService<DataService>();

4. Setup the routing for the LTI 1.3 platform endpoints:

app.UseLti13PlatformCore();

ILti13CoreDataService

There is no default ILti13CoreDataService implementation to allow each project to store the data how they see fit.

The ILti13CoreDataService interface is used to manage the persistance of most of the data involved in LTI communication.

All of the internal services are transient and therefore the data service may be added at any scope (Transient, Scoped, Singleton).

Defaults

Routing

Default routes are provided for all endpoints. Routes can be configured when calling UseLti13PlatformCore().

app.UseLti13PlatformCore(config => {
    config.AuthorizationUrl = "/lti13/authorization";
    config.JwksUrl = "/lti13/jwks";
    config.TokenUrl = "/lti13/token";
    return config;
});

ILti13PlatformService

The ILti13PlatformService interface is used to get the platform details to give to the tools.

There is a default implementation of the ILti13PlatformService interface that uses a configuration set up on app start. It will be configured using the IOptions pattern and configuration. The configuration path for the service is Lti13Platform:Platform.

Examples:

{
    "Lti13Platform": {
        "Platform": {
            "Guid": "server-id",
            ...
        }
    }
}

builder.Services.Configure<Platform>(x => { x.Guid = "server-id"; ... });

The Default implementation can be overridden by adding a new implementation of the ILti13PlatformService interface.

builder.AddLti13PlatformCore()
	.WithLti13PlatformService<CustomPlatformService>();

ILti13TokenConfigService

The ILti13TokenConfigService interface is used to get the token details for the tools.

There is a default implementation of the ILti13TokenConfigService interface that uses a configuration set up on app start. It will be configured using the IOptions pattern and configuration. The configuration path for the service is Lti13Platform:Token.

Examples

{
    "Lti13Platform": {
        "Token": {
            "Issuer": "https://<mysite>",
            ...
        }
    }
}

builder.Services.Configure<Lti13PlatformTokenConfig>(x => { x.Issuer = "https://<mysite>"; ... });

The Default implementation can be overridden by adding a new implementation of the ILti13TokenConfigService interface.

builder.AddLti13PlatformCore()
	.WithLti13TokenConfigService<CustomTokenConfigService>();

Important: The Issuer is required for the default token service to load.

Configuration

Platform

The platform information to identify the platform server, contacts, etc.

Guid

A stable locally unique to the iss identifier for an instance of the tool platform. The value of guid is a case-sensitive string that MUST NOT exceed 255 ASCII characters in length. The use of Universally Unique IDentifier (UUID) defined in RFC4122 is recommended.

ContactEmail

Administrative contact email for the platform instance.

Description

Descriptive phrase for the platform instance.

Name

Name for the platform instance.

Url

Home HTTPS URL endpoint for the platform instance.

ProductFamilyCode

Vendor product family code for the type of platform.

Version

Vendor product version for the platform.

Token Config

The configuration for handling of tokens between the platform and the tools.

Issuer

A case-sensitive URL using the HTTPS scheme that contains: scheme, host; and, optionally, port number, and path components; and, no query or fragment components. The issuer identifies the platform to the tools. An issuer is required.

TokenAudience

The value used to validate a token request from a tool. This is used to compare against the 'aud' claim of that JWT token request. If not provided, the token endpoint url will be used as a fallback.

MessageTokenExpirationSeconds Default: 300

The expiration time of the lti messages that are sent to the tools.

AccessTokenExpirationSeconds Default: 3600

The expiration time of the access tokens handed out to the tools.

Message Extensions

The LTI specs allow for messages to be extended with custom data. This is handled by adding Populators in the setup of the platform. To extend the message, create an interface with the properties that will be used to extend the message, and create a Populator<T> to fill those properties when the request for that message is generated.

Multiple populators can be added to the same interface. Multiple interfaces can be added to the same message type. The populator interface properties support the System.Text.Json attributes for serialization.

interface ICustomMessage
{
    [JsonPropertyName("https://purl.imsglobal.org/spec/lti/claim/custom")]
    public IDictionary<string, string>? Custom { get; set; }
}

class CustomPopulator: Populator<ICustomMessage>
{
	public override async Task PopulateAsync(ICustomMessage obj, MessageScope scope, CancellationToken cancellationToken = default)
    {
        obj.Custom = obj.Custom ?? new Dictionary<string, string>
		{
			{ "key", "value" }
		};
        
        ...
    }
}

builder.Services
    .AddLti13PlatformCore()
    .ExtendLti13Message<ICustomMessage, CustomPopulator>("LtiResourceLinkRequest");

Custom Messgage Types

LTI allows for message types not defined officially in any spec. A custom message type can be defined between tools and platforms. This is handled here by extending a message type name it with the interfaces and populators it needs.

interface ICustomMessage
{
    [JsonPropertyName("https://purl.imsglobal.org/spec/lti/claim/custom")]
    public IDictionary<string, string>? Custom { get; set; }
}

class CustomPopulator: Populator<ICustomMessage>
{
	public override async Task PopulateAsync(ICustomMessage obj, MessageScope scope, CancellationToken cancellationToken = default)
    {
        obj.Custom = obj.Custom ?? new Dictionary<string, string>
		{
			{ "key", "value" }
		};
        
        ...
    }
}

builder.Services
    .AddLti13PlatformCore()
    .ExtendLti13Message<ICustomMessage, CustomPopulator>("CustomMessage");

Terminology

Platform The platform is the server that is launching the tool. The platform is like a school or company and the tool has the content for the school or comapny to use.

Tool The tool is the application that is being launched by the platform. The tool has content to be launched. A relationship needs to be formed before a platform can launch anything in a tool.

Deployment A deployment is a specific instance of a tool in a platform. A platform may 'deploy' a tool multiple times (e.g. the district is the platform and has a different deployment of a tool for each school). Even if there is only going to be one instance of a tool in a platform, a single deployment is still required.

Context A context is a group of LTI links. In school terminology, a context may be a class or a course. A context may have resources from multiple tools.

ResourceLink A resource link is a link to a resource in a tool. The resource link is the object that is launched by the platform. Multiple resource links may be added to a single context.

Membership A membership is a relationship between a user and a context. The membership is used to determine what roles a user has in a context.

User A user is a person that is using the platform. The user may have a membership multiple contexts.

Attempt An attempt defines a user's interaction with a resource link.

LineItem A line item like a 'column' in a gradebook. It may or may not be tied to a ResourceLink and a ResourceLink may have 0 or more LineItems associated with it.

Grade A grade is a score for a user for a LineItem.

ServiceToken A service token is an identifier for a token given to a tool to access a service. It is used to avoid replay attacks and can be removed once the expiration date has elapsed.