Security for Scalable Registration, Authentication, and Authorization, published by HL7 International - Security WG. This guide is not an authorized publication; it is the continuous build for version 2.0.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/HL7/fhir-udap-security-ig/ and changes regularly. See the Directory of published versions

Registration

The requirements in this section are applicable to both consumer-facing and B2B apps and the servers that support them.

Before FHIR data requests can be made, Client application operators SHALL register each of their applications with the Authorization Servers identified by the FHIR servers with which they wish to exchange data.  Client applications SHALL use the client_id assigned by an Authorization Server in subsequent authorization and token requests to that server.

Authorization Servers SHALL support dynamic registration as specified in the UDAP Dynamic Client Registration profile with the additional options and constraints defined in this guide. Confidential clients that can secure a secret MAY use this dynamic client registration protocol as discussed further below to obtain a client_id. Other client types SHOULD follow the manual registration processes for each Authorization Server. Future versions of this guide may add support for dynamic client registration by public clients which cannot protect a private key.

The dynamic registration workflow is summarized in the following diagram:

Software Statement

To register dynamically, the client application first constructs a software statement as per section 2 of UDAP Dynamic Client Registration.

The software statement SHALL contain the required header elements specified in Section 1.2.3 of this guide and the JWT claims listed in the table below.  The software statement SHALL be signed by the client application operator using the signature algorithm identified in the alg header of the software statement and with the private key that corresponds to the public key listed in the client’s X.509 certificate identified in the x5c header of the software statement.

Example

Client Credentials

Example software statement, prior to Base64URL encoding and signature, for a B2B app that is requesting the use of the client credentials grant type (non-normative, the “.” between the header and claims objects is a convenience notation only):

{
  "alg": "RS256",
  "x5c": ["MIEF.....remainder omitted for brevity"]
}.{
  "iss": "http://example.com/my-b2b-app",
  "sub": "http://example.com/my-b2b-app",
  "aud": "https://oauth.example.net/register",
  "exp": 1597186041,
  "iat": 1597186341,
  "jti": "random-value-109a3bd72"
  "client_name": "Acme B2B App",
  "contacts": ["mailto:b2b-operations@example.com"],
  "grant_types": ["client_credentials"],
  "token_endpoint_auth_method": "private_key_jwt",
  "scope": "system/Patient.read system/Procedure.read"
}

Authorization Code

Example software statement, prior to Base64URL encoding and signature, for a B2B app that is requesting the use of the client credentials grant type (non-normative, the “.” between the header and claims objects is a convenience notation only):

{
  "alg": "RS256",
  "x5c": ["MIEF.....remainder omitted for brevity"]
}.{
  "iss": "http://example.com/my-user-b2b-app",
  "sub": "http://example.com/my-user-b2b-app",
  "aud": "https://oauth.example.net/register",
  "exp": 1597186054,
  "iat": 1597186354,
  "jti": "random-value-f83f37a29"
  "client_name": "Acme B2B User App",
  "redirect_uris": ["https://b2b-app.example.com/redirect"],
  "contacts": ["mailto:b2b-operations@example.com"],
  "logo_uri": "https://b2b-app.example.com/B2BApp.png",
  "grant_types": ["authorization_code", "refresh_token"],
  "response_types": ["code"],
  "token_endpoint_auth_method": "private_key_jwt",
  "scope": "user/Patient.read user/Procedure.read"
}

Request Body

The registration request for use of either grant type is submitted by the client to the Authorization Server’s registration endpoint.

POST /register HTTP/1.1
Host: oauth.example.net
Content-Type: application/json

{
   "software_statement": "...the signed software statement JWT...",
   "certifications": ["...a signed certification JWT..."]
   "udap": "1"
}

The Authorization Server SHALL validate the registration request as per Section 4 of UDAP Dynamic Client Registration. This includes validation of the JWT payload and signature, validation of the X.509 certificate chain, and validation of the requested application registration parameters.

If a new registration is successful, the Authorization Server SHALL return a registration response with a 201 Created HTTP response code as per Section 5.1 of UDAP Dynamic Client Registration, including the unique client_id assigned by the Authorization Server to that client app. Since the UDAP Dynamic Client Registration profile specifies that a successful registration response is returned as per Section 3.2.1 of RFC 7591, the authorization server MAY reject or replace any of the client’s requested metadata values submitted during the registration and substitute them with suitable values.

If a new registration is not successful, e.g. it is rejected by the server for any reason, the Authorization Server SHALL return an error response as per Section 5.2 of UDAP Dynamic Client Registration.

Inclusion of Certifications and Endorsements

Authorization Servers MAY support the inclusion of certifications and endorsements by client application operators using the certifications framework outlined in UDAP Certifications and Endorsements for Client Applications. Authorization Servers SHALL ignore unsupported or unrecognized certifications.

Authorization Servers MAY require registration requests to include one or more certifications. If an Authorization Server requires the inclusion of a certain certification, then the Authorization Server SHALL communicate this by including the corresponding certification URI in the udap_certifications_required element of its UDAP metadata.

An example template application to declare additional information about the client application at the time of registration is described in Section 7.3 of this guilde.

Modifying and Cancelling Registrations

Within a trust community, the client URI in the Subject Alternative Name of an X.509 certificate uniquely identifies a single application and its operator over time. Thus, a registered client application MAY request a modification of its registration with an Authorization Server by submitting another registration request to the same Authorization Server’s registration endpoint with a software statement containing a certificate corresponding to the same trust community and with the same iss value as was used in the original registration request. An Authorization Server accepting such a request SHALL only update the registration previously made in the context of the corresponding trust community, as detailed in the next paragraph, and SHALL NOT overwrite an existing registration made in the context of a different trust community.

If an Authorization Server receives a valid registration request with a software statement containing a certificate corresponding to the same trust community and with the same iss value as an earlier software statement but with a different set of claims or claim values, or with a different (possibly empty) set of optional certifications and endorsements, the server SHALL treat this as a request to modify the registration parameters for the client application by replacing the information from the previous registration request with the information included in the new request. For example, an Application operator could use this mechanism to update a redirection URI or to remove or update a certification. If the registration modification request is accepted, the Authorization Server SHOULD return the same client_id in the registration response as for the previous registration. If it returns a different client_id, it SHALL cancel the registration for the previous client_id.

If an Authorization Server receives a valid registration request with a software statement that contains an empty grant_types array from a previously registered application as per the previous paragraph, the server SHOULD interpret this as a request to cancel the previous registration. A client application SHALL interpret a registration response that contains an empty grant_types array as a confirmation that the registration for the client_id listed in the response has been cancelled by the Authorization Server.

If the Authorization Server returns the same client_id in the registration response for a modification request, it SHOULD also return a 200 OK HTTP response code. If the Authorization Server returns a new client_id in the registration response, the client application SHALL use only the new client_id in subsequent transactions with the Authorization Server.