With your Challenger Medallion socketed, the Hammer of Proving is ready. Challenge a prospective Commander and pillage Caiatl's Tribute Chest at the end of a Battleground to disrupt their Rite of Proving. The Battlegrounds playlist may be found in the Director under Vanguard missions.
Caiatl's emissaries flood Sol with ceremonial Gold, a custom during the Era of Conquest. Conquered worlds are enriched to ease defeat and afford the opportunity to challenge officers for representation within the Cabal's leadership.