Java: Send OTP with an Android SMS Gateway API

Hub C: android sms gateway api send OTP from Java. Cornerstone: Android SMS gateway API. Product: OTP verification. C sibling (same JSON): C send OTP. Keys: secure API keys in env.

Priced by devices and SMS send volume. You use your own phone and operator SMS credit.

If the OTP servlet and the Friday blast share a device nickname, you do not have two-factor. You have a queue argument at 18:00.

HttpClient is not a Java SMS SDK

POST JSON, Authorization Bearer, read the message id. Confirm POST /api/v1/messages in Developer Center. No Maven coordinate we sell, no “Complete Java SDK,” no JNI modem kit.

Named OTP device, hashed challenge

Store hash + expiry + attempt count. Compare on verify. Do not log the plaintext code. OTP priority queue. If last-seen is stale, fail closed — offline queue behavior.

Lane table: OTP vs MMS vs promo

One POST is not login complete

HTTP 200 is accept. Gate the UX on DLR or a conservative timeout plus inbound if you use reply codes. API delivery reports.

Bearer in env, not the WAR

Environment on the app server. Never a properties file in git. REST samples on PHP and C# are the same contract — not language SDKs.

Failed logins still spend the SIM

Priced by devices and SMS send volume. You use your own phone and operator SMS credit. Cooldown after resend. Attackers will burn airtime and platform volume if you have no cap. We do not refund operator tariffs.

Shape of a send

Illustrative only — confirm fields in Developer Center:

HttpRequest req = HttpRequest.newBuilder(URI.create(sendUrl))
    .header("Authorization", "Bearer " + System.getenv("SMS_GATEWAY_TOKEN"))
    .header("Content-Type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString(json))
    .build();
// persist message id; do not treat 200 as delivered

Checklist

• Named OTP device.
• Hash + expiry stored.
• Key in env.
• Idempotency on resend.
• No MMS for login.
• Last-seen check before send.
• No Java SDK branding.
• Developer Center checked.
• Resend cooldown.
• Canary staff MSISDN.

Next steps

Read OTP verification and pricing. The JVM is fast. The SIM still has a ceiling.