Function extract_user_info 

pub fn extract_user_info(
    config: &OAuthProviderConfig,
    userinfo_json: &Value,
    email_json: Option<&[Value]>,
) -> Result<OAuthUserInfo, ServiceError>

Extract normalized user info from a provider’s userinfo JSON response.

email_json is an optional array of email objects (GitHub /user/emails format) used when the primary userinfo endpoint doesn’t include the email.