currently after oauth succeeds backend redirects to FRONTEND_URL env var
but, different frontend implementations may have a different path to be redirected, and they all may use the same backend server
to make our soln more generic, the frontend will specify callback URL as a query param, when it initiates the o-auth flow
but how will backend store this cb URL, because, the control is handed over to external o-auth server.. and our backend code only gets back control, when the external provider calls our endpoint
so we can use the "state" variable for this communication
Specifies any string value that your application uses to maintain state between your authorization request and the authorization server's response. The server returns the exact value that you send as a name=value pair in the URL query component (?) of the redirect_uri after the user consents to or denies your application's access request.
You can use this parameter for several purposes, such as directing the user to the correct resource in your application, sending nonces, and mitigating cross-site request forgery. Since your redirect_uri can be guessed, using a state value can increase your assurance that an incoming connection is the result of an authentication request. If you generate a random string or encode the hash of a cookie or another value that captures the client's state, you can validate the response to additionally ensure that the request and response originated in the same browser, providing protection against attacks such as cross-site request forgery.
this is the equivalent link for github oauth
How to do this with nestjs/passport ? try StackOverflow link
Additional Todo: why this does not exist in official
@nestjs/passportdocs ? May be create an issue, or even a PR to their docs ..