Build
Say on-chain that a GitHub account is yours, and point at a proof only that account could publish. From then on, a bounty for your merged work pays the wallet you claimed, not an address someone else wrote in a file.
Case does not matter: the contract lowercases it, the same way GitHub does.
Whoever signs the transaction is who claims the login. One wallet, one login.
A gist of yours, or a repository of yours whose README contains your address. The page checks it before asking you to sign.