[Feature Request]: Be able to implement an async Custom Storage

[stemlaur]

Is your feature request related to a problem? Please describe.

Currently, the library allows to implement a custom storage, but it is limited to synchronous implementation, a developer should be able to implement an async custom storage returning Promises.

Describe the solution you'd like

It would be awesome to be able to create a custom storage like this one:

import { AbstractSecurityStorage } from 'angular-auth-oidc-client';

@Injectable()
export class AsyncStorageService implements AbstractSecurityStorage {

  read(key: string): Promise<any> {
    return await ...;
  }

  write(key: string, value: any): Promise<void> {
    await ...
  }

  remove(key: string): Promise<void> {
    await ...
  }

  clear(): void {
    await ...
  }
}

The library should check if the return object is a promise and await it if it is.

[jhpetersen]

Same same for me: i would like to store security data within a local SQLite db, but as all read/write operations are asynchronous, it is impossible to implement a custom storage provider for that use case.

Furthermore the hasStorage() method within BrowserStorageService could be problematic if the provided custom storage provider does not rely on default Storage interface..

[jhpetersen]

I would have liked to propose a PR, but just realized that synchronous calls to StoragePersistenceService read/write/remove/clear methods spreads over a lot of services/classes and these in turn are also synchronous methods, and so on.

So i assume implementing an async storage provider will result in huge effort to convert most parts of this library to async code, and thus will be a major/breaking change.

So the question to the creators/maintainers of this library: is this somehow on the roadmap? (is there any roadmap at all? 🤔 😉) Or do you see any possibility how to achieve this with less effort / limited changes?