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

Consumer-Facing

This guide supports consumer-facing client applications using the authorization code grant type.

Consumer-facing client applications SHALL obtain an access token for access to FHIR resources by following the OAuth 2.0 authorization code grant flow, with the additional options and constraints discussed below.

Obtaining an authorization code

The workflow for obtaining an authorization code is summarized in the following diagram:

Client applications SHALL request an authorization code as per Section 4.1.1 of RFC 6749, with the following additional constraints. Client applications that also support the SMART App Launch IG are NOT REQUIRED to include a launch scope or launch context requirement scope. Client applications and servers MAY optionally support UDAP Tiered OAuth for User Authentication to allow for cross-organizational or third party user authentication as described in Section 6.

Servers SHALL handle and respond to authorization code requests as per Section 4.1.2 of RFC 6749.

Client applications and Authorization Servers SHALL conform to the additional constraints for authorization code flow found in Section 7.1 of this guide.

Obtaining an access token

The workflow for obtaining an access token is summarized in the following diagram:

Client applications SHALL exchange authorization codes for access tokens as per Section 4.1.3 of RFC 6749, with the following additional options and constraints.

Client applications SHALL include a code_verifier parameter and value in the token request as per Section 4.5 of RFC 7636.

Constructing Authentication Token

If the client app has registered to authenticate using a private key rather than a shared client_secret, then the client SHALL use its private key to sign an Authentication Token as described in this section, and include this JWT in the client_assertion parameter of its token request as described in Section 5.1 of UDAP JWT-Based Client Authentication and detailed further in Section 4.2.2 of this guide. For clients and servers that also support the SMART App Launch IG, this overrides the requirement for the client to use HTTP Basic Authentication with a client_secret in Section 7.1.3 of the SMART App Launch IG v1.0.0.

Authentication Tokens submitted by client apps SHALL conform to the general JWT header requirements above and SHALL include the following parameters in the JWT claims defined in Section 4 of UDAP JWT-Based Client Authentication:

Authentication JWT Claims
iss	required	The application's client_id as assigned by the Authorization Server during the registration process
sub	required	The application's client_id as assigned by the Authorization Server during the registration process
aud	required	The FHIR Authorization Server's token endpoint URL
exp	required	Expiration time integer for this authentication JWT, expressed in seconds since the "Epoch" (1970-01-01T00:00:00Z UTC).
iat	required	Issued time integer for this authentication JWT, expressed in seconds since the "Epoch"
jti	required	A nonce string value that uniquely identifies this authentication JWT. See Section 1.2.4 for additional requirements regarding reuse of values.

The maximum lifetime for an Authentication Token SHALL be 5 minutes, i.e. the value of exp minus the value of iat SHALL NOT exceed 300 seconds. The Authorization Server MAY ignore any unrecognized claims in the Authentication Token. The Authentication Token SHALL be signed and serialized using the JSON compact serialization method.

Submitting a token request

For client applications authenticating with a shared secret, the client application and server SHALL follow the token request and response protocol in Section 4.1.3 and Section 4.1.4 of RFC 6749.

Client applications authenticating with a private key and Authentication Token as per Section 4.2.1 SHALL submit a POST request to the Authorization Server’s token endpoint containing the following parameters as per Section 5.1 of UDAP JWT-Based Client Authentication. Client apps authenticating in this manner SHALL NOT include an HTTP Authorization header or client secret in its token endpoint request. The token request SHALL include the following parameters:

Token request parameters
grant_type	required	Fixed value: authorization_code
code	required	The code that the app received from the Authorization Server
redirect_uri	conditional	The client application's redirection URI. This parameter SHALL be present only if the redirect_uri parameter was included in the authorization request in Section 4.1, and their values SHALL be identical.
client_assertion_type	required	Fixed value: urn:ietf:params:oauth:client-assertion-type:jwt-bearer
client_assertion	required	The signed Authentication Token JWT
udap	required	Fixed value: 1

Server processing of token requests

An Authorization Server receiving token requests containing Authentication Tokens as above SHALL validate and respond to the request as per Sections 6 and 7 of UDAP JWT-Based Client Authentication.

The Authorization Server SHALL return an error as per Section 4.6 of RFC 7636 if the client included a code_challenge in its authorization request but did not include the correct code_verfier value in the corresponding token request.

For all successful token requests, the Authorization Server SHALL issue access tokens with a lifetime no longer than 60 minutes.

Refresh tokens

This guide supports the use of refresh tokens, as described in Section 1.5 of RFC 6749. Authorization Servers MAY issue refresh tokens to consumer-facing client applications as per Section 5 of RFC 6749. Client apps that have been issued refresh tokens MAY make refresh requests to the token endpoint as per Section 6 of RFC 6749. Client apps authenticate to the Authorization Server for refresh requests by constructing and including an Authentication Token in the same manner as for initial token requests.