Obtain a SMART Backend Services access token using the system-level client credentials flow with a signed JWT client assertion and use it to access a FHIR server as a backend service
domain: hl7.org/fhir/smart-app-launch · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Retrieve the FHIR server's .well-known/smart-configuration to discover the token_endpoint and supported token_endpoint_auth_methods_supported values
Build a signed JWT client assertion with iss=client_id, sub=client_id, aud=token_endpoint, jti, and exp; sign with RS384 or ES384
POST to token_endpoint with grant_type=client_credentials, client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer, client_assertion=<JWT>, and scope=system/*.read
Extract the access_token from the response and attach it as a Bearer token in subsequent FHIR API calls
Re-request a token before expiry (check expires_in) to maintain continuous access without user interaction
Known gotchas
grant_type must be client_credentials and client_assertion_type must be exactly urn:ietf:params:oauth:client-assertion-type:jwt-bearer — any deviation causes immediate 400 errors
System-level scopes use the system/ prefix, not patient/ or user/; requesting patient/ scopes in a backend services flow will be rejected
The JWKS URL registered during app enrollment must be publicly reachable by the authorization server at token request time; firewall or localhost URLs will cause key fetch failures
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