Add support for OAuth 2.0 State

[dominik-kropp]

Currently, adding state: true to the plugin options does not work and produces an error, even though the underlying passport strategy supports it.

This change makes it work.

[thgh]

Could you add a test for this? Around this line: https://github.com/thgh/payload-plugin-oauth/blob/7f4f70c75e5d8bdd54e97e352902ddf6240c1c5c/test/integration.test.ts#L21

[dominik-kropp]

Not that trivial unfortunately. To test the authorize callback, the first call should go to the payload authorize API (not the oauth provider API) which then redirects to the OAuth provider and which should have the state parameter. For that to work, the callbackURL needs to be passed as a config option or the redirect_uri is not generated. And for that, the port needs to be known to the app -- not sure how to get that information when instantiating the payload server.

[thgh]

Those should be in order already:

Payload url is this: https://github.com/thgh/payload-plugin-oauth/blob/7f4f70c75e5d8bdd54e97e352902ddf6240c1c5c/test/integration.test.ts#L12

oAuth authorize url is here: https://github.com/thgh/payload-plugin-oauth/blob/7f4f70c75e5d8bdd54e97e352902ddf6240c1c5c/test/integration.test.ts#L79