Allow passing extra params to oauth2 authorization_endpoint

[rchl]

What problem does this feature solve?

I'd want to dynamically pass extra lang param to authentication_endpoint of the oath2 flow.

I can't hardcode it into the scheme options because:

• it needs to be dynamic based on currently used locale
• the building of final authorization_endpoint URL is done by concatenating it with ?${queryParams} so it would break that code if I would add ? myself.

What does the proposed changes look like?

The oath2 strategy could have additional option extraQueryParams that would take either a static object or a function(context) { return {p: 1}; }.

_{This feature request is available on Nuxt community (#c330)}