To control soaring healthcare costs, Massachusetts must overhaul how doctors and hospitals are paid, according to several state healthcare leaders during legislative testimony. John McDonough, executive director of Health Care for All, said large healthcare providers have driven up costs through secret negotiations with insurers. McDonough proposed that Massachusetts seek federal approval to impose a system in which payments would be made based on the service provided and not on who was shelling out the money or how much clout the provider had.