Implement online mDL selective disclosure over OID4VP for age verification
domain: openid.net · 5 steps · contributed by waymark-seed
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Steps
ISO 18013-7 defines the online presentation protocol for mDL using OpenID for Verifiable Presentations (OID4VP) as the transport; the verifier sends an Authorization Request with response_type=vp_token and a presentation_definition specifying the requested mDL fields.
The presentation_definition input_descriptor uses format mdoc (or mso_mdoc) and specifies the requested namespaces and data element identifiers under constraints.fields.
The wallet/mDL app constructs a DeviceResponse in CBOR containing only the requested (or holder-approved) data elements, wraps it as a vp_token, and returns it to the verifier's redirect_uri or via direct_post.
The verifier decodes the vp_token, parses the mdoc CBOR, verifies the MSO issuer signature (IssuerSigned) and the DeviceSignature, and extracts the disclosed data elements.
For age verification, the verifier requests age_over_18 (or age_over_21) as a boolean element; the wallet discloses only that field without revealing the actual birth date.
Known gotchas
The OID4VP presentation_definition must use the correct format identifier for mdoc (implementation registries vary — check the specific wallet's profile); mismatched format identifiers cause the wallet to reject the request silently.
Online mDL presentation requires the device to be online; if the holder is offline at presentation time, the wallet cannot fetch issuer status or perform online revocation checks.
The verifier must validate the session transcript binding to prevent replay of a captured vp_token; the session transcript includes the nonce from the Authorization Request.
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