HerokuからApache HttpClientでOutbound IP固定で通信

HerokuアプリからSalesforce APIを発行する際、Salesforce側に許可IPを設定したいのでProximoアドオン(HTTP Proxy)でOutbound IPを固定した
Inboundも固定したいならQuotaGuard Static(のMicro以上)の方がいいかも

ProximoのURLは以下の形式
http://＜Proximoユーザ名＞:＜Proximoパスワード＞@proxy-＜IPアドレス＞.proximo.io
認証が必要なのでそれなりのコーディングを行った

PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
// https://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html 2.4. Multithreaded request execution
// TODO: Tuning
HttpClientBuilder httpClientBuilder = HttpClients.custom().setConnectionManager(poolingHttpClientConnectionManager);

URL proxyUrl = new URL(＜環境変数PROXIMO_URLの値＞);
String proxyHostString = proxyUrl.getHost();
int proxyPort = proxyUrl.getPort();
HttpHost proxyHost = proxyPort != -1 ? new HttpHost(proxyUrl.getHost(), proxyPort) : new HttpHost(proxyUrl.getHost());
String proxyUserInfo = proxyUrl.getUserInfo();
String proxyUsername = proxyUserInfo.substring(0, proxyUserInfo.indexOf(':'));
String proxyPassword = proxyUserInfo.substring(proxyUserInfo.indexOf(':') + 1);
httpClientBuilder.setProxy(proxyHost);
httpClientContext = HttpClientContext.create();
CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
credentialsProvider.setCredentials(new AuthScope(proxyHost), new UsernamePasswordCredentials(proxyUsername, proxyPassword));
httpClientContext.setCredentialsProvider(credentialsProvider);
BasicScheme basicScheme = new BasicScheme();
basicScheme.processChallenge(new BasicHeader(AUTH.PROXY_AUTH, "Basic"));
BasicAuthCache basicAuthCache = new BasicAuthCache();
basicAuthCache.put(proxyHost, basicScheme);
httpClientContext.setAuthCache(basicAuthCache);

CloseableHttpClient httpClient = httpClientBuilder.build(); // 同じ相手に何度も通信するならcloseすることなく使い回した方が接続やhandshakeにかかる時間を節約できる

HttpGet request = new HttpGet(XXX);
try (CloseableHttpResponse response = httpClient.execute(request, httpClientContext)) {
    String responseBody = EntityUtils.toString(response.getEntity());
    StatusLine statusLine = response.getStatusLine();
    if (statusLine.getStatusCode() != HttpStatus.SC_OK) {
        log.error("XXX failed. statusLine={}, responseBody={}", statusLine.toString(), responseBody);
        throw new RuntimeException("XXX failed");
    }
    ★responseBodyを使って処理
}