[data-plane]: Make OIDCDiscoveryConfig more resistant against invalid OIDC discovery config

[creydr]

Currently the loading of the OIDC config from the discovery endpoint is not very robust and fails on an invalid OIDC config (e.g. when the issuer was configured in the k8s config without https and thus the query results in a 404):

eventing-kafka-broker/data-plane/core/src/main/java/dev/knative/eventing/kafka/broker/core/oidc/OIDCDiscoveryConfig.java

Lines 60 to 84 in 02be94e

	return webClient
	.getAbs("https://kubernetes.default.svc/.well-known/openid-configuration")
	.bearerTokenAuthentication(kubeConfig.getAutoOAuthToken())
	.send()
	.compose(res -> {
	logger.debug("Got raw OIDC discovery info: " + res.bodyAsString());
	try {
	ObjectMapper mapper = new ObjectMapper();
	OIDCInfo oidcInfo = mapper.readValue(res.bodyAsString(), OIDCInfo.class);
	oidcDiscoveryConfig.issuer = oidcInfo.getIssuer();
	return webClient
	.getAbs(oidcInfo.getJwks().toString())
	.bearerTokenAuthentication(kubeConfig.getAutoOAuthToken())
	.send();
	} catch (JsonProcessingException e) {
	logger.error("Failed to parse OIDC discovery info", e);
	return Future.failedFuture(e);
	}
	})
	.compose(res -> {

This should be changed (e.g. status code checking) and the OIDCDiscoveryConfig fail the returned future correctly in such a case (e.g. with an additional exception, which can then be handled by the caller).