Add docs guide: Proxying Between Zuplo Gateways

[zuplo-integrations-app]

Summary

• New docs guide covering how to proxy requests between Zuplo gateway projects
• Addresses content gap identified in zuplo/www#2660 — users building federated/product-of-products topologies need guidance on URL Forward patterns, auth propagation, and 522 troubleshooting
• Fact-checked against Zuplo documentation with all claims verified

Content

Title: Proxying Between Zuplo Gateways
Type: Docs Guide
Slug: guides/proxying-between-zuplo-gateways
File: docs/guides/proxying-between-zuplo-gateways.mdx

Sections covered

1. When this pattern makes sense (product-of-products, BFF, tenant routing, migration)
2. Three patterns: URL Forward Handler, custom fetch handler, Federated Gateways
3. Auth propagation (credential forwarding, shared secret, Upstream Zuplo JWT)
4. Surfacing upstream errors instead of 522 (with code examples)
5. Custom domains across the fleet
6. Cost considerations for fan-out architectures
7. Troubleshooting matrix (522 with no logs, 522 only for Zuplo targets, content type mismatches)

Sidebar updates

• Added to sidebar.guides.ts under "Routing & Backends"
• Added to sidebar.ts under "Development > Guides"

Fact-Check Results

• 31 claims verified against Zuplo docs (timeout values, handler configs, policy syntax, API patterns)
• 3 corrections applied: fixed zuploapp.com → zuplo.app (canonical domain), corrected 522 timeout description to distinguish TCP connection vs TCP ACK scenarios, clarified Federated Gateways as enterprise add-on
• 0 code issues: all TypeScript/JSON examples verified syntactically correct with proper Zuplo API imports
• Content review applied: renamed .md → .mdx for consistency, fixed broken api-keys.mdx → api-keys.md link, added custom-code and authentication tags, improved troubleshooting heading clarity

Closes zuplo/www#2660

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview, Comment	May 15, 2026 5:41pm