Authorization

This chapter describes how authorization works and what decisions impact the design of a use case.

OAuth2 Scopes and Presentation Definition Mapping

Scope design

When designing a system that uses OAuth2, you have to decide how scopes map to resources that the client will attempt to access. "Resource access" is typically a specific REST-style HTTP operation on a specific URL, e.g. POST /products/staplers/1. Things to consider when designing scopes are discussed in this section.

Broad v.s. narrow scopes

Broad scopes are generally high level e.g., a scope that gives access to a certain use case or larger group of resources. Narrow scopes are often low-level e.g., a scope that gives read access to a specific resource, limited set of resources or operations. Examples scopes for an employee that's authorized to buy supplies for their employer:

How scopes are mapped to operations on resources influences:

Broad, high-level Scopes

High-level, broad scopes typically give access to an entire use case, service, or group of resources. Checks that are executed before an access token is issued are limited to the Verifiable Credentials the client can present.

A real-life example of a broad scope is the Nuts eOverdracht use case, which specifies the following scopes:

However, when a resource is accessed, the system needs to verify that the scope gives access to the specific resource operation.

This type of scope is supported by the Nuts node.

Narrow, low-level Scopes

Narrow, low-level scopes typically give access to specific operations on specific resources, e.g., reading a specific patient's medical summary.

This type of scope is not supported by the Nuts node, because:

Another consideration is that using low-level scopes, moves most authorization decisions to the access token issuance. This is viable and supported by the Nuts node, but complicated: it requires the vendor to implement a REST API that understands Presentation Definitions.

Policies: Mapping Scope to Authentication Subject

Due to the ongoing development of personal authentication methods and associated protocols, the Nuts node currently only supports the OAuth2 vp_token grant for production. User authentication via OpenID4VP is experimental and not intended for production. It's still required to pass user claims within the token request if a data exchange contains PII (Personally Identifiable Information) and/or medical data (e.g., Social Security Number or EHR records)

Mapping document

This section contains an example of a presentation definition mapping document as it could be specified by a use case. The Presentation Definition is described more in detail in AuthN using Verifiable Credentials.

{
  "zorgtoepassing": {
    "organization": {
      "format": {
        "ldp_vc": {
          "proof_type": [
            "JsonWebSignature2020"
          ]
        },
        "ldp_vp": {
          "proof_type": [
            "JsonWebSignature2020"
          ]
        },
        "jwt_vc": {
          "alg": [
            "ES256"
          ]
        },
        "jwt_vp": {
          "alg": [
            "ES256"
          ]
        }
      },
      "id": "pd_any_care_organization",
      "name": "Care organization",
      "purpose": "Finding a care organization for authorizing access to medical metadata",
      "input_descriptors": [
        {
          "id": "id_nuts_care_organization_cred",
          "constraints": {
            "fields": [
              {
                "path": [
                  "$.type"
                ],
                "filter": {
                  "type": "string",
                  "const": "NutsOrganizationCredential"
                }
              },
              {
                "id": "organization_name",
                "path": [
                  "$.credentialSubject.organization.name",
                  "$.credentialSubject[0].organization.name"
                ],
                "filter": {
                  "type": "string"
                }
              },
              {
                "id": "organization_city",
                "path": [
                  "$.credentialSubject.organization.city",
                  "$.credentialSubject[0].organization.city"
                ],
                "filter": {
                  "type": "string"
                }
              }
            ]
          }
        }
      ]
    }
  }
}

AuthN using Verifiable Credentials

To successfully negotiate an OAuth2 access token, the token issuer (OAuth2 Authorization Server) will ask the client to present Verifiable Credentials. Nuts uses DIF Presentation Exchange for requesting and presenting credentials during authentication. It's used by the service-to-service (vp_token bearer) OAuth2 flow. It is also used by Discovery Services to restrict what can be registered on it.

Presentation Definition

The party requesting a presentation, typically during access token negotiation, provides a Presentation Definition to the credential wallet. The Presentation Definition specifies which credentials the wallet must provide. If the wallet can't fulfill the definition, access token negotiation will fail.

NutsCareOrganization example

Below is an example Presentation Definition specifying a NutsOrganizationCredential, not restricted to a specific issuer. It specifies the following:

{
  "format": {
    "ldp_vc": {
      "proof_type": [
        "JsonWebSignature2020"
      ]
    }
  },
  "id": "pd_any_care_organization",
  "name": "Care organization",
  "purpose": "Finding a care organization for authorizing access to medical metadata",
  "input_descriptors": [
    {
      "id": "id_nuts_care_organization_cred",
      "constraints": {
        "fields": [
          {
            "path": [
              "$.type"
            ],
            "filter": {
              "type": "string",
              "const": "NutsOrganizationCredential"
            }
          },
          {
            "path": [
              "$.issuer"
            ],
            "filter": {
              "type": "string"
            }
          },
          {
            "id": "organization_name",
            "path": [
              "$.credentialSubject.organization.name"
            ],
            "filter": {
              "type": "string"
            }
          },
          {
            "id": "organization_city",
            "path": [
              "$.credentialSubject.organization.city"
            ],
            "filter": {
              "type": "string"
            }
          }
        ]
      }
    }
  ]
}

The identifiers used in the field constraints will be available in the token introspection result. The key will be the field id and the value will be the value in the credential that matches the path.

Authorizing Access Tokens through Presentation Exchange

See the DIF Presentation Exchange specification for more information.

Credential Trust

Authentication on Nuts heavily depends on trusted credential issuers: any attribute, relevant to the security model of the use case should be verifiable. E.g., if a party claims to be a care organization, it should be able to present a Verifiable Credential to prove it. The same applies to a user presenting their name or claiming to be a care professional.

Who should be the trusted issuer for a specific Verifiable Credential depends on the context. But generally, issuers are authoritative registries (e.g. Dutch CIBG) or even state-issued (PID of natural persons).

Credential types are defined in the credential catalog. It is the normative source for credential definitions.

In practice, there are the following credential issuers:

X509Credential with UZI server certificates

Care organizations authenticate with an X509Credential, created from their UZI server certificate. This page explains how the certificate ends up in the credential, and what a use case's Discovery Service and policy definitions need to check.

The X509Credential is defined in the credential catalog (normative). For did:x509 and the background, see RFC023. For how to create one, see "Get an X509Credential from a UZI certificate" in Implementing a Nuts v2 Use Case.

Why X509Credential

HealthcareProviderCredential: the HealthcareProviderCredential (credential catalog, draft) is seen as the next version of the X509Credential. It is built from the same UZI server certificate through did:x509, but contains the URA as a typed identifier instead of the raw certificate fields. This page covers only the X509Credential.

Which CA to trust

UZI server certificates are issued by the UZI register (CIBG), under the PKIoverheid hierarchy. The X509Credential's issuer is a did:x509 DID, which contains the fingerprint (ca-fingerprint) of one CA in the certificate's chain. A definition trusts a CA by listing its fingerprint.

The CA that issues the UZI server certificates is called the UZI CA below. It is an intermediate CA itself: the lowest CA in the chain, directly above the UZI server certificate (marked ◄ in the trees).

Production G1
Staat der Nederlanden Private Root CA - G1
└── Staat der Nederlanden Private Services CA - G1
    ├── UZI-register Private Server CA G1                ◄ ca-fingerprint
    │   └── UZI server certificate
    └── KPN, DigiCert, QuoVadis, ... (other providers, no URA)

Production G4 (from 12 November 2026)
Staat der Nederlanden - G4 Root Priv G-TLS - 2024
└── Staat der Nederlanden - G4 Intm Priv G-TLS SYS - 2024
    ├── UZI Server - G4 PKIo Priv G-TLS SYS - 2025       ◄ ca-fingerprint
    │   └── UZI server certificate
    └── KPN, DigiCert, Digidentity, ... (other providers, no URA)

Test G1
TEST Zorg CSP Private Root CA G1
└── TEST Zorg CSP Level 2 Private Services CA G1
    └── TEST UZI-register Private Server CA G1           ◄ ca-fingerprint
        └── UZI server certificate

Acceptance G4
ACCEPTATIE Zorg CSP - G4 Root Priv G-TLS - 2024
└── ACCEPTATIE Zorg CSP - G4 Intm Priv G-TLS SYS - 2024
    └── ACCEPTATIE UZI Server - G4 Priv G-TLS SYS - 2025 ◄ ca-fingerprint
        └── UZI server certificate
UZI CA Environment ca-fingerprint (SHA-256, base64url)
UZI-register Private Server CA G1 Production vdhg746H4rLH67NN1unhdxo6PF3shQunCA4-KQTb2Jc
UZI Server - G4 PKIo Priv G-TLS SYS - 2025 Production, from 12 November 2026 sDTL__yv54TtrvSf7601TtvHgj2NZSLT2m-Okf8oqkI
TEST UZI-register Private Server CA G1 Test GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A
ACCEPTATIE UZI Server - G4 Priv G-TLS SYS - 2025 Test, acceptance svKzNxhS07V1dKkekWOZV0d6Ao7_qvjqXegWB32YjZE

Rules for definitions

A definition should trust exactly the UZI CAs for its environment:

A definition should not trust:

Deviate only with a reason, and write it down in the use case's IG.

From certificate to credential

These certificate fields end up in the X509Credential:

Certificate field Credential field Contains
subject.O credentialSubject.subject.O Name of the care organization
subject.L credentialSubject.subject.L City
san.otherName credentialSubject.san.otherName UZI number, URA and more, see below

The URA in san.otherName

san.otherName is one string with seven parts, separated by -:

<OID CA>-<version>-<UZI number>-<pass type>-<URA>-<role>-<AGB code>
2.16.528.1.1007.99.2110-1-900025039-S-90000382-00.000-00000000
Part Example Meaning
OID CA 2.16.528.1.1007.99.2110 The CIBG
Version 1 Version of this format
UZI number 900025039 Number of the certificate holder, same as subject.serialNumber
Pass type S Always S (server)
URA 90000382 The care organization's URA ("abonneenummer")
Role 00.000 Always 00.000
AGB code 00000000 The care organization's AGB code

To get the URA in a definition, use a pattern with a capture group on this field. The node then returns only the captured part, e.g. in search results and token introspection:

{
  "id": "organization_ura",
  "path": ["$.credentialSubject.san.otherName"],
  "filter": { "type": "string", "pattern": "^[0-9.]+-\\d+-\\d+-S-(\\d+)-00\\.000-\\d+$" }
}

Appendix: examples

Fictional care organization "De Regenboog" in Hengelo, URA 90000380, with a UZI server certificate from the TEST UZI CA.

did:x509 DID

did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344
Part Meaning
sha256:GwlhBZuE… ca-fingerprint: SHA-256 hash of the DER-encoded TEST UZI-register Private Server CA G1 certificate, base64url-encoded
subject:O:De%20Regenboog:L:Hengelo Certificate fields subject.O (OID 2.5.4.10) and subject.L (OID 2.5.4.7), URL-encoded
san:otherName:… Certificate field san.otherName (OID 2.5.5.5), with the URA 90000380

Resolved DID document

The node builds the DID document from the certificate chain in the credential's JWT header (x5c):

{
  "@context": ["https://www.w3.org/ns/did/v1"],
  "id": "did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344",
  "controller": ["did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344"],
  "verificationMethod": [
    {
      "id": "did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344#0",
      "type": "JsonWebKey2020",
      "controller": "did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344",
      "publicKeyJwk": { "kty": "RSA", "n": "<modulus>", "e": "AQAB" }
    }
  ],
  "assertionMethod": ["did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344#0"]
}

X509Credential (JWT payload)

{
  "iss": "did:x509:0:sha256:GwlhBZuEFlSHXSRUXQuTs3_YpQxAahColwJJj35US1A::subject:O:De%20Regenboog:L:Hengelo::san:otherName:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344",
  "sub": "did:web:nuts.vendor.example:iam:deregenboog",
  "vc": {
    "@context": ["https://www.w3.org/2018/credentials/v1", "https://nuts.nl/credentials/v1"],
    "type": ["VerifiableCredential", "X509Credential"],
    "credentialSubject": {
      "id": "did:web:nuts.vendor.example:iam:deregenboog",
      "subject": { "O": "De Regenboog", "L": "Hengelo" },
      "san": { "otherName": "2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344" }
    }
  }
}

The JWT header contains the full certificate chain in x5c.

Sources for the CA certificates: production and acceptance on zorgcsp.nl.

OAuth2 Flows and Wallets

Nuts supports a custom OAuth2 flow for acquiring an access token: the service-to-service flow.

Service-to-Service flow

Credentials that are presented during this flow are subject to legal organizations (e.g. registered care organizations).

This flow uses a custom grant type called vp_token-bearer. Presentation requests always and only target organization wallets. User claims can be passed as tokens. If and how the user claims correspond to the organization attestations is done by the authorization step.

The flow is secured with DPoP (optional). See "Security controls" for a detailed description.

Security controls

The following security controls are used by the OAuth2 flows:

Access Policy

Anti-patterns