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Discovery Proxy

The problem​

HAPI FHIR JPA does not serve /.well-known/smart-configuration natively. SMART clients send discovery requests to the FHIR base URL (iss), so without this filter they get a 404.

SmartDiscoveryProxyFilter​

SmartDiscoveryProxyFilter is an OncePerRequestFilter that intercepts GET /fhir/.well-known/smart-configuration on the HAPI server and forwards it to the Auth Server:

@Override
protected void doFilterInternal(HttpServletRequest req,
                                  HttpServletResponse res,
                                  FilterChain chain) {
    String targetUrl = authServerUrl + "/.well-known/smart-configuration";
    HttpResponse<String> proxyResponse = httpClient.send(
        HttpRequest.newBuilder(URI.create(targetUrl)).GET().build(),
        HttpResponse.BodyHandlers.ofString()
    );
    res.setContentType("application/json");
    res.getWriter().write(proxyResponse.body());
}

Registering on HAPI​

Option A — Spring filter registration:

@Bean
public FilterRegistrationBean<SmartDiscoveryProxyFilter> discoveryProxy() {
    FilterRegistrationBean<SmartDiscoveryProxyFilter> reg =
            new FilterRegistrationBean<>();
    reg.setFilter(new SmartDiscoveryProxyFilter("http://localhost:9000"));
    reg.addUrlPatterns("/.well-known/*");
    reg.setOrder(1);
    return reg;
}

Option B — nginx reverse proxy:

location /.well-known/smart-configuration {
    proxy_pass http://localhost:9000/.well-known/smart-configuration;
}

Testing​

# Should return the same JSON as:
curl http://localhost:8080/fhir/.well-known/smart-configuration
curl http://localhost:9000/.well-known/smart-configuration