Code review comment: We could make this a normal GET that just uses the values from the persisted settings.

Code under review:
private HttpResponse handlePOST(Path path, HttpRequest request) {
        if (path.matches("/application/v4/tenant/{tenant}")) return createTenant(path.get("tenant"), request);
        if (path.matches("/application/v4/tenant/{tenant}/key")) return addDeveloperKey(path.get("tenant"), request);
        if (path.matches("/application/v4/tenant/{tenant}/secret-store/{name}/validate")) return validateSecretStore(path.get("tenant"), path.get("name"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}")) return createApplication(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/platform")) return deployPlatform(path.get("tenant"), path.get("application"), "default", false, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/pin")) return deployPlatform(path.get("tenant"), path.get("application"), "default", true, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/application")) return deployApplication(path.get("tenant"), path.get("application"), "default", request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/key")) return addDeployKey(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/submit")) return submit(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}")) return createInstance(path.get("tenant"), path.get("application"), path.get("instance"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploy/{jobtype}")) return jobDeploy(appIdFromPath(path), jobTypeFromPath(path), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/platform")) return deployPlatform(path.get("tenant"), path.get("application"), path.get("instance"), false, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/pin")) return deployPlatform(path.get("tenant"), path.get("application"), path.get("instance"), true, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/application")) return deployApplication(path.get("tenant"), path.get("application"), path.get("instance"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/submit")) return submit(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/job/{jobtype}")) return trigger(appIdFromPath(path), jobTypeFromPath(path), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/job/{jobtype}/pause")) return pause(appIdFromPath(path), jobTypeFromPath(path));
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/deploy")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request); 
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/reindex")) return reindex(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/reindexing")) return enableReindexing(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/restart")) return restart(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/suspend")) return suspend(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), true);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}/deploy")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request); 
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}/restart")) return restart(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        return ErrorResponse.notFoundError("Nothing at " + path);
    }

Line commented on: if (path.matches("/application/v4/tenant/{tenant}/secret-store/{name}/validate")) return validateSecretStore(path.get("tenant"), path.get("name"), request);

Revised code:
private HttpResponse handlePOST(Path path, HttpRequest request) {
        if (path.matches("/application/v4/tenant/{tenant}")) return createTenant(path.get("tenant"), request);
        if (path.matches("/application/v4/tenant/{tenant}/key")) return addDeveloperKey(path.get("tenant"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}")) return createApplication(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/platform")) return deployPlatform(path.get("tenant"), path.get("application"), "default", false, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/pin")) return deployPlatform(path.get("tenant"), path.get("application"), "default", true, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/deploying/application")) return deployApplication(path.get("tenant"), path.get("application"), "default", request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/key")) return addDeployKey(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/submit")) return submit(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}")) return createInstance(path.get("tenant"), path.get("application"), path.get("instance"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploy/{jobtype}")) return jobDeploy(appIdFromPath(path), jobTypeFromPath(path), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/platform")) return deployPlatform(path.get("tenant"), path.get("application"), path.get("instance"), false, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/pin")) return deployPlatform(path.get("tenant"), path.get("application"), path.get("instance"), true, request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/deploying/application")) return deployApplication(path.get("tenant"), path.get("application"), path.get("instance"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/submit")) return submit(path.get("tenant"), path.get("application"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/job/{jobtype}")) return trigger(appIdFromPath(path), jobTypeFromPath(path), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/job/{jobtype}/pause")) return pause(appIdFromPath(path), jobTypeFromPath(path));
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/deploy")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request); 
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/reindex")) return reindex(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/reindexing")) return enableReindexing(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/restart")) return restart(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/instance/{instance}/environment/{environment}/region/{region}/suspend")) return suspend(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), true);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}/deploy")) return deploy(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request); 
        if (path.matches("/application/v4/tenant/{tenant}/application/{application}/environment/{environment}/region/{region}/instance/{instance}/restart")) return restart(path.get("tenant"), path.get("application"), path.get("instance"), path.get("environment"), path.get("region"), request);
        return ErrorResponse.notFoundError("Nothing at " + path);
    }