Ensures correct HTTPS scheme for OAuth callback URL generation behind reverse proxies.

This plug checks (in order):

1. X-Forwarded-Proto header (nginx/apache standard)
2. Explicit :phoenix_kit, :oauth_base_url config
3. Endpoint URL configuration

Usage

Automatically included in OAuth controller. No manual setup required.

Configuration (Optional)

For edge cases where headers aren't available:

config :phoenix_kit,
  oauth_base_url: "https://example.com"