Invoice support on pools/exchanges side

Btw, it puzzles me why nobody implemented invoices support. The wallet has this functionality since 1.1. It would solve all the issues with withdrawals, which are the biggest pain now. The flow is simple - a user request a withdrawal, perform some auth dance (password, 2fa, phone call etc), gets an unique url at the end. Then they sends an invoice to this address via https, a services verifies it and signs, user’s wallet finalizes. One click experience, no setup on the customer side, less wallet calls on the service side (only receive).