OID4VC: Demo creates new credential_supported metadata entry for each issuance (BUG)

[timbl-ont]

Each time the demo is used to issue a new credential, a call is made to create a new credential_supported entry. The effect is that the metadata will include the same credential type multiple times (after the first issuance).

For some wallets this appears to work ok, but it breaks the Sphereon wallet, which attempts to make a credential request for each entry of the issued credential type in the credential metadata. Effectively it only works the first time a credential is issued.

To fix this, the demo will need to persist a flag to indicate that the metadata has been created and also persist the supported_cred_id for subsequent issuance.

Note: the holder binding needs to be set to did:jwk to support the Sphereon wallet. Otherwise did:key is used, which is not supported by the plugin.