Add getOAuthHelpers method

[DeanMauro]

This PR makes OAuthHelpers available outside of the fetch method (i.e. in a worker's RPC methods).

Problem

this.env.OAUTH_PROVIDER gets populated in OAuthProviderImpl.fetch(), so if we try to use it in a worker's RPC methods, for example, it will always be undefined.

const oauthProvider = new OAuthProvider({});

export default class extends WorkerEntrypoint<AuthWorkerEnv> {
  async fetch(request: Request) {...}

  async checkClient(id: string) {
    // ERROR because this.env.OAUTH_PROVIDER isn't set yet
    const existingClient = await this.env.OAUTH_PROVIDER.lookupClient(id);

    // SUCCESS
    const existingClient = await oauthProvider.getOAuthHelpers(this.env).lookupClient(id);
  }
}

Solution

We need a method OAuthProvider.getOAuthHelpers(env: any) that initializes and retrieves OAuthHelpers directly from the provider.

❌ We can't put the method directly onto the provider because it will get exposed, intentionally or otherwise, as a public RPC method on the worker.

export class OAuthProvider {
  ...
 getOAuthHelpers(env: any) {
      return this.#impl.getOAuthHelpers(env);
  };
}

✅ But if we use a Symbol to name the method, it appears on the provider like we want, but excluded from the worker's RPC methods.

export class OAuthProvider {
  ...
  [getOAuthHelpersSymbol](env: any): OAuthHelpers {
    return this.#impl.getOAuthHelpers(env);
  }
}

export function getOAuthHelpers(provider: OAuthProvider, env: any): OAuthHelpers {
  return provider[getOAuthHelpersSymbol](env);
}

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[DeanMauro]

@mattzcarey - Can you give this a review?

@kentonv - Found a neat way to add methods to the provider without exposing them over RPC

[kentonv]

Hate to say but getters can, in fact, be invoked over RPC. It's an explicit feature of the RPC system.

You could perhaps create a separate freestanding function getOAuthHelpers(provider :OAuthProvider), and this function could work by reading a property whose name is a private Symbol.

[DeanMauro]

Ahh thought I was being clever here. Must have messed something up when testing.

Switched it over to a Symbol and getOAuthHelpers(provider: OAuthProvider, env: any) method. Confirmed this is working as expected. Thanks!