At the bottom of builders page you have (or can configure) a "Force selected builds" and "Force All Builds" menus If you don't have it you can configure it with
users = [(user, password)]
authz_cfg=authz.Authz(auth=BasicAuth(users),
forceBuild = 'auth',
forceAllBuilds = True,
cancelPendingBuild = True,
stopBuild = True,
stopAllBuilds = True,
)
You can read more about Authz in the documentation