Fix Github provider

[jmschneider]

Fix issue with using jsonMiddleware for form encoded data. Update documentation to indicate that client_secret is required.

[pi0]

This line is affecting all providers! If formMiddleware is required we can add an optional parameter like addAuthorize(strategy, { json: true } = {}) and conditionally use either form for json middleware

[jmschneider]

Currently, the addAuthorize function is only called by the github provider. The problem is the _handleCallback method in the oauth2 scheme. It looks like it used to send json data but at some point was changed to send form data. Whenever this was changed, the serverMiddleware was not updated to use the form middleware. Currently, I could not get the github provider to work without this change.

As a side not, this was an issue I ran into with the laravel.passport provider as well and was a major reason I did not use the addAuthorize function. If we also had the authorization request send the full req.body instead of just req.body.code it could potentially be reused for the laravel.passport provider.

[pi0]

pending to prevent breaking changes

[jmschneider]

After looking at the oauth2 scheme, I think it might make sense to add redirect_uri, response_type and grant_typeto the data sent by the server middleware. If it is all data that is intentionally included in the front end authentication token request it would make sense that we would also want to include it in the backend authentication token request.

[pi0]

Merging as a hotfix because

Currently, the addAuthorize function is only called by the github provider.