Add dynamic client registration

[jasonpaulos]

I've started using this library with Solid to authenticate against inrupt.net and solid.community, and since Solid is decentralized it requires apps to dynamically register with the provider. Both AppAuth-Android and AppAuth-iOS provide support for client registration, so I added the Javascript and native code required to take advantage of that. I would really like to get this accepted so that others don't have to start from scratch with this too!

Description

I've added a new library function, register, which can be used to obtain a client id and secret for subsequent calls to authorize and other library functions.

I've tested the functionality on iOS and Android, and everything is working properly.

I did end up modifying the eslint settings, since it was giving me errors when using == null to check if parameters had been passed to register, and since it was limiting the number of statements that could be used in an arrow function, which affected the tests.

Steps to verify

import { register } from 'react-native-app-auth';

const res = await register({
  issuer: 'https://inrupt.net',
  redirectUrls: ['com.myapp.id:/oauthredirect']
});
// res is now { clientId: '...', clientSecret: '...', ... }

Let me know if there's anything I can do to help get this approved.

[kadikraman]

Thanks so much for the PR, this is great! Just a small update before I can merge it. We've recently updated the error messaging descriptions to make them consistent across platforms, so it would e great if we could update the errors in this PR before merging it

service_configuration_fetch_error - could not fetch the service configuration
authentication_failed - user authentication failed
token_refresh_failed - could not exchange the refresh token for a new JWT
registration_failed (new) - could not register

[jasonpaulos]

Thank you @kadikraman! I have updated the error messages as you suggested.

[kadikraman]

LGTM 👍

[kadikraman]

Released in v5.0.0 🎉