oid4vci-credential-offer

To implement an OID4VCI credential offer flow, you use the `credential_offer` parameter or `credential_offer_uri` to initiate issuance, then process the offer to construct the correct token request for obtaining the verifiable credential.

The `authorization_code` grant type requires standard user authentication, while the `pre-authorized_code` grant type allows the issuer to pre-authorize the wallet to receive credentials, streamlining the token endpoint request process without additional user interaction.

A wallet retrieves the offer details from the `credential_offer_uri`, determines the applicable grant type, and constructs a token endpoint request according to RFC6749 specifications to obtain the access token needed for credential retrieval.

Error handling for `pre-authorized_code` token requests follows RFC6749 specifications, requiring the wallet to parse token endpoint error responses and manage exceptions when the credential offer or authorization fails.

Use the inline `credential_offer` parameter for smaller payloads passed directly, and use `credential_offer_uri` when the offer payload is large or needs to be fetched separately by the wallet to avoid exceeding URL length limits.