DID

Decentralized identifiers (DIDs) are a new type of identifier that enables verifiable, decentralized digital identity. DID document associated with DIDs contains a verification method. The owner of a DID can use the private key associated and anyone can verify that the owner control the public key.

One advantage is that this allows our document issuance flow to not rely on the need to write on blockchain, eliminating the need for gas fees.

You can read more about DID on wikipedia or deep dive into w3c specifications.