feat(Authentication) enable authentication strategies to contribute OASEnhancer

[dougal83]

Extend AuthenticationStrategy to implement OASEnhancer.

Example usage:
App > jwt-strategy.ts:

// ...
@bind(asAuthStrategy, asSpecEnhancer)
export class JWTAuthenticationStrategy
  implements AuthenticationStrategy, OASEnhancer {
  // ...
  modifySpec(spec: OpenApiSpec): OpenApiSpec {
    return mergeSecuritySchemeToSpec(spec, this.name, {
      type: 'http',
      scheme: 'bearer',
      bearerFormat: 'JWT',
    });
  }
}

App > application.ts:

// ...
// authentication
this.add(createBindingFromClass(JWTAuthenticationStrategy));

See also #4554
Impl. #3669

Checklist

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

[dougal83]

@derdeka Would this satisfy #3669? PTAL

[jannyHou]

@dougal83 🙇‍♀ Thank you again for creating a follow-up PR for the security spec. I left a few suggestions.
sorry for the delay again 😅 finished the auth migration PR so I have enough bandwidth to help you apply this feature this month

[dougal83]

Restricted to a single SecuritySchemeObject as I didn't see eventuality of adding multiple.

[bajtos]

Thank you @dougal83 for the pull request, I appreciate the effort you are putting into this initiative ❤️

I like that your pull request includes test coverage to verify that security schemas are correctly contributed. What I like even more is that we have two examples of real-world security schemas that we can use when users come asking about examples 👍

I'd like to discuss few aspects of the proposed implementation, see my comments below.

[jannyHou]

🙇‍♀ LGTM when CI passes. Thanks @bajtos and @raymondfeng for joining the discussion, extending the enhancer class is much better than having a separate class(my original proposal).

I will refactor https://github.com/strongloop/loopback-next/tree/master/examples/access-control-migration/src/components/jwt-authentication accordingly as well.

[bajtos]

I find this new version so much more elegant 👏

Can you please add a tsdoc comment and a unit test for mergeSecuritySchemeToSpec?

[dougal83]

The simplicity of the PR is down to great architectural design by the Loopback Team. It was surprising how little work was required in the end! Keep up the great work! ❤️

[jannyHou]

🎉 🎉 Merged! Thank you @dougal83 for the effort and patience, next target is #4365. (design kudos goes to Miroslav and Raymond :p)