Extract the jwt authentication to a local component for the auth migration example app

[jannyHou]

Suggestion

After creating the demo for JWT authentication in loopback4-shopping-example, and applied a similar auth system in loopback-example-access-control, we think it's time to extract the jwt authentication system into a separate extension package, so that:

• jwt related services, bindings can be packed as a component
• people can easily mount the component when they need a simple working authentication system, they can customize and enhance the system later
• separating the component from example apps will give people a much more clear idea of what's the core of authentication

Use Cases

This extension will provide a basic jwt authentication system as a component. It's used when people want to see a demo of how to leverage an existing authentication strategy, or need a prototype of authentication to plugin and add code on it(like authorization).

Examples

In your application file, mount the authentication component like

// find a better name
import {JWT_AUTH_COMPONENT} from '@loopback/jwt-authentication-extension'
export class MyApplication extends BootMixin(
  ServiceMixin(RepositoryMixin(RestApplication)),
) {
this.component(JWT_AUTH_COMPONENT)
}

Then you can secure controller endpoints with @authenticate('jwt').

Details to figure out by the story owner: how to provide the custom User model. Include it in the component? Or define it in the app and integrate it with the component?

Acceptance criteria

• Extract jwt.auth.strategy.ts, jwt.service.ts, security.spec.ts, user.service.ts, keys.ts and bindings in application.ts from feat: add access control migration app #4571 into a component
• Add unit tests for services, and acceptance tests
• Refactor the migration app in feat: add access control migration app #4571 to leverage the component and update corresponding doc
• After finishing step 3, we should have a better understanding of how to refactor the shopping example, if we have bandwidth, refactor it in a separate story, and also update the existing auth tutorials if needed (issue Refactor Shopping Example: simulate ACLs with LB4 authorization #4522)

[jannyHou]

• UPDATE: to simplify the story, let's first make it a local refactor for the auth migration example app: extract jwt authentication into a local component for it.