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Credentials

Modeling W3C Verifiable Credentials in FHIR

This document describes how healthcare data, modeled in FHIR, can be presented in the form of a W3C Verifiable Credential (VC).

Content Definition

Any time we want to present healthcare data in the form of a VC, we must first make some use-case-specific decisions:

  1. Define a set of required and optional FHIR content resources (e.g., Immunization or Observation) that must be packaged and presented together
  2. Decide how to bind these FHIR content resources to a person's external identity, via FHIR identity resources (e.g., Patient)

Once we make these decisions, we can construct a VC with a credential subject as follows:

  • credentialSubject with these top level elements:
    • fhirVersion: a string representation of the semantic FHIR version the content is represented in (e.g. 1.0.* for DSTU2, 4.0.* for R4, where * is a number, not a literal asterisk)
    • fhirBundle: a FHIR Bundle resource of type "collection" that includes all required FHIR resources (content + identity resources)

Resulting payload structure:

{
  "@context": ["https://www.w3.org/2018/credentials/v1"],
  ...
  "credentialSubject": {
    "fhirVersion": "4.0.1",
    "fhirBundle": {
      "resourceType": "Bundle",
      "type": "collection",
      "entry": [
        ...
      ]
    }
  }
}

Below we focus on the Health Card use case, but the same approach to forming VCs out of FHIR can be applied to other use cases, too.

Modeling a "Health Card"

A "Health Card" is a VC that conveys results about one discrete condition -- in this case a single COVID-19 serology study, encompassing IgG and IgM detection. Other cards could convey details of a RT-PCR test for COVID-19, a clinical diagnosis of COVID-19, TDAP vaccination, and so on.

According to the procedure above, we start with decisions about FHIR content resources and identity resources:

  • Which FHIR content resources need to be conveyed in a package? For the diagnostic results, we need:

    • Observation with effectiveTime and a COVID-19 IgM result
    • Observation with effectiveTime and a COVID-19 IgG result
    • DiagnosticReport from COVID-19 testing, that conveys an overall conclusion (optional)
  • What FHIR identity resources do we need to bind the FHIR content resources to an external identity system? We should support two presentation contexts:

    • For Online Presentation, we expect that the consumer will present the VC to an organization that has a pre-existing relationship with the consumer, so it's sufficient to bind the VC to a real-world name and verified phone number:
      • Patient with name and phone number
      • (possibly) Patient with alternate sets of attributes for other use-cases
    • For In-person Presentation, we expect that the consumer will present the VC at an in-person interaction alongside a physical photo ID, so it's sufficient to bind the VC to a facial image that matches the consumer's physical photo ID
      • Patient with name and a photo of sufficient size and quality

Since we need to support two presentation contexts, we'll need to generate two VCs (one per presentation context), so the consumer can share the appropriate VC for any given context.

Health Card Examples