Dapp-a-day 9: Reverse ("Demanding") Token Auction

Each weekday leading up to devcon2, Nexus will highlight a dapp, library, or package (something with a dappfile) as a promotion of our toolchain and as case studies for other developers. Yesterday's Post

Today's dapp is a variant on yesterday's token auction.

https://github.com/makerdao/demanding-auction

From the README:

A reverse auction is a bidding contest in which bidders offer to buy diminishing quantities of the sold token for a fixed quantity of the buying token.
The 'normal' way to implement this is to take the sold token into escrow at the start of the auction and to give it to the winning bidder at the end of the auction (e.g. token-auction).
An alternative is to supply the sell-token on demand: the sell-token is supplied by another contract at the time of auction close and is never taken into escrow. This adds an extra layer of trust, in that bidders need to verify the demandable contract, but is useful when the sold token supply has to be inflated to meet the winning bid.
An example of this usage is in Maker, during the debt auction. In this auction, Maker seeks to acquire a fixed quantity of Dai in return for as little MKR as possible. The Dai is used to pay off debt incurred in liquidating an underwater CDP; the MKR is provided by inflating the total MKR supply.