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Integrating RCS with File Management Systems: APIs, Webhooks, and SDK Examples

UUnknown

2026-02-05

10 min read

Developer guide to integrating RCS with file systems: encrypted, auditable file links over mobile RCS with API, webhook, and SDK examples.

Deliver encrypted file links over RCS: why it matters in 2026

Hook: If your team still emails presigned links or pastes Dropbox URLs into chat, you’re losing control — of security, auditability, and speed. By 2026, teams expect secure, trackable file delivery directly to mobile devices with near-real-time confirmations. Integrating modern RCS APIs with file-management systems gives you that: encrypted file links, delivery and read receipts, and immediate confirmation workflows across Android and iPhone where RCS E2EE is now broadly available.

The evolution and opportunity (2024–2026)

RCS has matured rapidly since Universal Profile 3.0, and late-2025/early-2026 trends are decisive: major vendors moved to support MLS-based end-to-end encryption, carriers started enabling E2EE for cross-platform conversations, and messaging aggregator APIs now expose both rich RCS features and webhooks for event-driven integrations.

This matters to developers because RCS is no longer “rich SMS” — it’s a programmable mobile messaging channel that supports cards, suggested actions, and secure payloads. When combined with signed, short-lived file links and clear delivery receipts, RCS becomes a secure transport for exchanging sensitive files to field engineers, auditors, and customers.

High-level architecture: how the pieces fit

File storage — S3-compatible storage or an enterprise file system storing the binary behind an ID.
Link generator — server component that creates per-recipient, time-limited, cryptographically-protected links (presigned + encrypted token).
RCS provider / aggregator — exposes REST APIs / SDKs to send RCS messages and webhooks to receive events (delivery/read receipts, replies).
Webhook consumer — serverless function or webhook endpoint that verifies provider signatures and records events into audit logs and ticketing systems.
Client handlers — mobile app or browser that opens the link, performs client-side decryption/verification if necessary, and displays file or triggers download.

Design goals and threat model (practical)

Design for:

Short-lived access — links expire quickly (60s–24h depending on sensitivity).
Per-recipient binding — token contains recipient and message ID so a leaked link can't be replayed.
Auditability — every send, delivery, open, and download is logged with cryptographic integrity.
Fallbacks — if RCS is unavailable, automatically downgrade to MMS/SMS with a narrower experience.

Threat vectors to mitigate:

Link interception — prevent with short TTL, per-user binding, and optional client-side decryption.
Webhook forgery — verify signatures (HMAC / JWT) from providers.
Misdelivery — include recipient identity in tokens and validate client-provided claims.

Step-by-step integration: from storage to RCS message

1) Register with an RCS aggregator and configure webhooks

Pick a provider that supports Universal Profile 3.x and E2EE (2026 requirement). Register a service, obtain API keys, and configure your webhook URL in the provider console. Set webhook events for delivery_receipt, read_receipt, message_reply, and message_status.

2) Secure storage and link generation

Strategy: generate a two-part token — a short-lived presigned URL for the object storage and a signed/encrypted access token bound to the recipient and message.

Example: Node.js code to create an AWS S3 presigned URL and embed it into a JWE-encrypted payload using the jose library.

// Node.js (simplified)
const { S3Client, GetObjectCommand } = require('@aws-sdk/client-s3');
const { getSignedUrl } = require('@aws-sdk/s3-request-presigner');
const { compactEncrypt } = require('jose');

const s3 = new S3Client({ region: 'us-east-1' });

async function generateSecureLink({ bucket, key, recipientId, recipientPubJwk }) {
  // 1) Generate presigned URL (short TTL)
  const presigned = await getSignedUrl(s3, new GetObjectCommand({ Bucket: bucket, Key: key }), { expiresIn: 300 });

  // 2) Build token payload bound to recipient / msg
  const payload = JSON.stringify({ url: presigned, recipient: recipientId, iat: Math.floor(Date.now()/1000) });

  // 3) Encrypt payload to recipient's public key (JWE)
  const epk = await compactEncrypt(new TextEncoder().encode(payload), await importJWK(recipientPubJwk, 'ECDH-ES'));

  return { presigned, token: epk };
}

Why both? The presigned URL is the actual transport; the JWE token allows the mobile client or server to prove link legitimacy and deliver additional metadata (audit_id, policy, checksum) without exposing secrets in the clear.

3) Send the RCS message with a rich card and the encrypted link

Send a rich RCS card that contains:

A card title/summary
An action button (open_url) that points to an internal redirect endpoint on your domain — this endpoint verifies the JWE and either redirects to the presigned URL or requires client-side decryption.
Suggested replies (Accept / Decline / Download Later) to capture confirmations via RCS quick replies

Example curl POST to a hypothetical provider API:

curl -X POST https://api.rcs-aggregator.example/v1/messages \
  -H "Authorization: Bearer ${API_KEY}" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+15551234567",
    "type": "rcs",
    "rcs": {
      "rich_card": {
        "title": "Secure File: report.zip",
        "description": "Encrypted report for project X.",
        "actions": [{
          "type": "open_url",
          "url": "https://files.example.com/rcs-open?token=${encodeURIComponent(token)}"
        }],
        "suggestions": ["Downloaded","Request Access"]
      }
    }
  }'

4) Implement the link verifier (server-side redirect)

The redirect endpoint must verify the token, check recipient binding, log the access event, then issue a 302 to the presigned URL or stream the object. If you require client-side decryption, return a small HTML app that performs the JWE decryption using the device key (only for enrolled devices).

// Express.js (simplified)
app.get('/rcs-open', async (req, res) => {
  const token = req.query.token;
  // 1) Decrypt token with server key (or verify JWE recipient)
  const payload = await decryptJWE(token); // returns { url, recipient, iat }

  // 2) Verify recipient == intended recipient (e.g., via query param or phone matching)
  if (!isAllowed(req, payload.recipient)) return res.status(403).send('Forbidden');

  // 3) Log access
  await auditLog({ type: 'link_open', recipient: payload.recipient, time: Date.now(), payloadHash: hash(payload) });

  // 4) Redirect to presigned URL
  return res.redirect(payload.url);
});

Webhook handling: capture delivery and confirmations

Providers call your webhook with events for message_sent, delivery_receipt, read_receipt, and user_reply. Always verify the signature and canonicalize timestamps to prevent replay attacks.

Webhook verification (HMAC SHA256 example)

// Node.js webhook handler (Express)
app.post('/webhooks/rcs', express.json(), async (req, res) => {
  const signature = req.header('X-RCS-Signature');
  const payload = JSON.stringify(req.body);

  if (!verifyHmac(payload, signature, process.env.RCS_WEBHOOK_SECRET)) {
    return res.status(401).send('Invalid signature');
  }

  // Process events
  for (const event of req.body.events) {
    switch(event.type) {
      case 'delivery_receipt':
        await recordDelivery(event.messageId, event.timestamp, event.status);
        break;
      case 'read_receipt':
        await recordRead(event.messageId, event.timestamp);
        break;
      case 'user_reply':
        await handleReply(event.messageId, event.from, event.text);
        break;
    }
  }

  res.status(200).send('ok');
});

Store mappings: messageId <-> fileId <-> recipient so you can correlate receipts to downloads for audit reports.

Client-side handling: mobile SDK and deep-link best practices

Two common patterns for clients:

Server-decrypt and redirect — easiest for BYOD. The server validates device identity (optional) then redirects to presigned URL.
Client-decrypt with device key — stronger binding: the JWE is encrypted to the device's public key; only the device can decrypt. Use enrollments and secure key stores (Android Keystore / iOS Secure Enclave).

Android (intent handler) example

Register an intent-filter for your universal link and handle the incoming deep link to validate and open the file. Use Android Keystore for decrypting JWE.

// Android (Kotlin) - handle intent in Activity
override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  val data = intent.data
  data?.let {
    val token = it.getQueryParameter("token") ?: return
    lifecycleScope.launch {
      val payload = decryptTokenWithKeystore(token)
      if (payload.recipient != currentUserId) {
        showForbidden()
        return@launch
      }
      // Open file (download or stream)
      openUrl(payload.url)
    }
  }
}

iOS (Swift) example

Handle universal links in scene delegate and use Secure Enclave for decryption when client-side decryption is required.

// iOS (Swift) - SceneDelegate
func scene(_ scene: UIScene, continue userActivity: NSUserActivity) {
  guard let url = userActivity.webpageURL else { return }
  if let token = URLComponents(url: url, resolvingAgainstBaseURL: false)?.queryItems?.first(where: { $0.name == "token" })?.value {
    Task {
      let payload = try await decryptTokenWithSecureEnclave(token)
      guard payload.recipient == currentUserId else { return }
      openUrl(payload.url)
    }
  }
}

Fallbacks and carrier considerations

Not every recipient will have RCS availability or E2EE enabled. Best practice:

Detect RCS capability from the provider response (capability queries) before sending.
If RCS unsupported, send an SMS with a narrower interaction — short link + OTP validation to claim the file.
Log the channel used for compliance and billing.

Security and compliance checklist

Encrypt links using JWE or signed JWT with recipient binding.
Use presigned URLs with minimal TTL and scope.
Verify webhooks (HMAC, signature, nonce) and keep replay windows small.
Audit every event (send, delivery, read, open, download) into immutable logs (WORM or append-only stores).
Data residency — place storage and webhooks in compliant regions; record region in audit logs.
Rotation and revocation — allow immediate revocation of links and rotate signing keys per policy.
Least privilege for S3 credentials and RCS provider API keys.

Observability, testing, and cost predictability

Instrument the flow end-to-end: unique correlation IDs in the message payload, log-level propagation, and a topology map in your observability tool (Prometheus, Datadog). Test with near-production datasets using carrier sandboxes and emulate network conditions.

Cost considerations: RCS provider bills by message and rich features, storage by GB/month, and egress for downloads. Optimize by serving the file over a CDN connected to your storage and by tuning presigned TTLs.

Advanced strategies and 2026 predictions

Trends to incorporate:

Wider E2EE adoption — with Apple and major carriers supporting MLS, expect guaranteed end-to-end security for RCS flows; design to take advantage of client-side decryption for highly sensitive files.
Carrier-side verification — carriers will surface device attestation signals that help you increase trust without extra friction.
Native SDKs — more RCS SDKs provide native mobile hooks for rich cards and event callbacks; prefer provider SDKs when they reduce complexity. See Pocket Edge Hosts for edge-friendly SDK and hosting patterns.
Zero-trust sharing — moving from link-based access to identity-based ephemeral grants (OIDC tokens embedded in messages) for higher assurance.

“By 2026, RCS plus secure link generation and verified webhooks becomes the fastest path to securely delivering files to mobile users while maintaining enterprise audit and compliance needs.”

Complete example: end-to-end flow summary

Engineer uploads file to S3; server stores fileId and metadata.
Server generates presigned URL + JWE token encrypted to recipient device public key.
Server sends RCS message via provider API with rich card and a deep link containing the token.
Provider delivers message; webhook sends delivery and read receipts to your webhook endpoint.
User taps the card; redirect endpoint verifies token and logs access; optionally the device performs client-side decryption; the download occurs over CDN.
Webhook events and storage access logs produce a complete audit trail for compliance.

Practical code and testing tips

Use provider sandboxes with test phone numbers and delivery simulation.
Automate tests that validate signature verification for webhooks and that tokens cannot be replayed.
Include synthetic monitoring that performs a full send-to-download cycle hourly for critical flows.

Actionable takeaways

Always bind links to recipient identity and use short TTLs (<= 5 minutes for sensitive files).
Encrypt metadata as a JWE and, when possible, encrypt to the device public key for end-to-end assurance.
Verify webhooks with HMAC/JWT and log cryptographically-signed audit events for compliance.
Implement graceful fallback to SMS/MMS with OTP verification when RCS is not available.
Instrument correlation IDs through storage, message send, webhooks, and client interactions for observability.

Next steps — practical checklist to ship in 30 days

Choose RCS aggregator with Universal Profile 3.x & E2EE support — enable webhooks.
Implement secure link generator (presigned + JWE) and a verification endpoint.
Implement send flow with rich cards and suggested replies; wire up webhook handler.
Build mobile deep-link handlers for Android/iOS and decide server vs client decryption.
Set up observability and an audit export to your GRC tool.

Conclusion & call-to-action

Integrating RCS with file-management systems unlocks a secure, trackable way to deliver files to mobile users while preserving compliance and developer-friendly automation. In 2026, with broad E2EE adoption and richer provider APIs, it's the right time to move from brittle link-sharing to a robust, auditable message + link architecture.

Ready to implement this in your environment? Start with a free developer sandbox from your RCS provider and use our checklist above. If you want a reference implementation, filesdrive.cloud provides an open-source starter kit (server + mobile handlers + webhook validator) optimized for secure RCS link delivery — sign up for a trial or contact our engineering team for a migration review.

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