feat(api-integration): add Nango webhook handling

[devin-ai-integration]

feat(api-integration): add Nango webhook endpoint

Summary

Adds a POST /webhook endpoint to crates/api-integration for receiving Nango auth webhooks. The endpoint verifies the X-Nango-Hmac-Sha256 signature against a configured secret and deserializes the payload into the existing hypr_nango::ConnectWebhook type.

Changes:

• New webhook.rs route with HMAC-SHA256 signature verification
• nango_webhook_secret (required String) added to IntegrationConfig and Env
• hmac and sha2 added as workspace dependencies
• Route registered at /webhook alongside existing /connect-session

Note: The handler currently logs the webhook event and returns { "status": "ok" } — it does not persist the connection_id. Persistence/callback logic will need to be added by the consumer.

Review & Testing Checklist for Human

• Signature comparison is not constant-time — verify_signature uses != on hex strings instead of hmac's built-in mac.verify() which does constant-time comparison. Evaluate whether this timing side-channel matters for your threat model.
• IntegrationConfig::new() defaults nango_webhook_secret to String::new() — if a caller forgets .with_webhook_secret(...), verification will silently use an empty secret. Consider whether the secret should be a required constructor parameter instead.
• ConnectWebhook type drops fields — Nango sends success, providerConfigKey, provider, authMode, environment etc. in auth webhooks, but the current ConnectWebhook struct in hypr_nango doesn't capture these. serde will silently ignore them, but you may want these fields (especially success and providerConfigKey) for production use.
• No persistence — the webhook logs but doesn't save the connection_id → end_user_id mapping, which the Nango docs say is the primary purpose of the webhook. Verify this is intentional scaffolding vs. an oversight.
• Verify the webhook works end-to-end by configuring a Nango environment webhook URL (e.g. via ngrok) and triggering a test connection flow.

Notes

Link to Devin run: https://app.devin.ai/sessions/67e3cd84b2784186b83fda3739d5891c
Requested by: @yujonglee

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[devin-ai-integration]

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Devin Review found 2 potential issues.

View 4 additional findings in Devin Review.

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Devin Review found 1 new potential issue.

View 5 additional findings in Devin Review.