fix(auth): set AuthStyleInParams for OAuth2

[masnwilliams]

TL;DR

Fixes the OAuth2 authentication flow by sending client credentials in the request body, as required by the provider.

Why we made these changes

The upstream OAuth2 provider expects the client_id and client_secret to be in the request parameters during the token exchange. The previous configuration sent them in the Authorization header, causing authentication to fail.

What changed?

• Set AuthStyle: oauth2.AuthStyleInParams in the oauth2.Config. This forces the credentials into the request body, allowing the token exchange to succeed.

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