Nebular: [Bug] Missing client_id in form-data of refresh_token request with NbOAuth2AuthStrategy

[PatrickHuetter]

Issue type

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• [X] bug report
• [ ] feature request

Issue description

Current behavior:
When nebular oauth2 parts want to refresh a token using _authorization_code_ grant/flow for login and _refresh_token_ for refresh, it fails because the request for the refresh_token endpoint doesn't contain the client_id as specified by the oauth2 spec.

Expected behavior:
The request for refreshing the token should contain the "client_id" in the form data of the _refresh_token_ request. This is also described here: https://www.oauth.com/oauth2-servers/access-tokens/refreshing-access-tokens/

Typically, refresh tokens are only used with confidential clients. However, since it is possible to use the authorization code flow without a client secret, the refresh grant may also be used by clients that don’t have a secret. If the client was issued a secret, then the client must authenticate this request. Typically the service will allow either additional request parameters client_id and client_secret, or accept the client ID and secret in the HTTP Basic auth header. If the client does not have a secret, then no client authentication will be present in this request.

Steps to reproduce:
Just setup a keycloak oauth2 server and configure nebular to use that with NbOAuth2AuthStrategy.
Login (this works) and wait until your token expires and watch nebular making the request to the token-endpoint with the refresh_token in chrome debug tools. You will see that it fails because the client_id is missing.

[PatrickHuetter]

UPDATE: I found a workaround if you're using keycloak as IDP.

Just set the client_secret to some random value. Because the nebular auth module is only including the client_id payload if both client_id and client_secret exists (that's the bug) and keycloak isn't checking the secret in authorization_code mode this seems to work.
https://github.com/akveo/nebular/blob/bc68d11b9278e7a9f1c5c77b20c269c6025c0e58/src/framework/auth/strategies/oauth2/oauth2-strategy.ts#L347