What promise did Harold Godwineson allegedly make to William I in Normandy?

According to contemporary Norman sources, such as the Bayeux Tapestry, Harold Godwineson was sent to Normandy by Edward the Confessor to confirm Duke William as the king's heir.12

During this visit, after being released from captivity by one of William's vassals and joining the duke on a military campaign in Brittany, Harold allegedly swore an oath of fealty to William. In this oath, Harold promised to support William’s claim to the English throne and to uphold Edward's bequest of the crown to the duke. William later used Harold's violation of this oath as a primary moral and political justification for his invasion of England in 1066.12