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Dynamic path templating for webhook destinations

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評価

難易度
5/5
見積もり時間
1週間以上
初心者へのやさしさ
35/100
issue の種類
機能追加
明瞭さ
おおむね明確
活発さ
静か
技術スタック
go
領域
backend-api-design

調査の方向性

Start by reading the webhook provider's existing Go text/template use for signing secrets and signature content. Then trace how destination URL configuration is validated and how delivery attempts construct requests; the payload does not name specific files or tests. Resolve the open choices around template inputs and failure behavior, and define tests for rendered paths and the stated guardrails before implementation.

索引モデルが issue の本文から書いたものです。

説明

enhancement
Problem / use case.

When a tenant initiates an operation, say a action.initiated event, tey often want the resulting webhook delivered to a per-operation callback path chosen at initiation time, e.g. https://app.example.com/actions/<uuid>/callback

From a developer-experience standpoint this is a very natural thing to reach for: "I just want Outpost to handle the retries, queuing and delivery of this one HTTP request, so why can't I just hand it the destination URL on the fly?" It's an intuitive ask, which is part of why it keeps coming up.

Today a webhook destination's url is fully static per destination. The only way to achieve a per-operation path is to create a throwaway destination for each operation and publish with destination_id. That means unbounded destination churn plus lifecycle and cleanup burden, which does not fit a high-volume "one callback per action" pattern.
It also fragments the portal/UI experience: instead of thousands of single-use destinations, each with its own isolated logs, delivery attempts, and metrics, templating keeps everything under a single stable destination. All the usual actions (viewing delivery history, retrying, inspecting attempts, editing config) then operate on one coherent destination rather than being scattered across per-operation throwaways.

Proposal

Allow the path portion of a webhook URL to be templated from event fields, while the scheme + host remain fixed static config. This reuses the Go text/template mechanism already used for signing secrets and signature content in the webhook provider.

Example destination confog:

config.url               = "https://app.example.com"
config.url_path_template = "/actions/{{.metadata.callback_id}}/callback"

Publishing an event with metadata.callback_id = "abc-123" delivers to:

https://app.example.com/actions/abc-123/callback

Retries, queuing and signing all continue to work exactly as they do today.

Why templated path, not arbitrary URL

A fully event-controlled URL, while much easier to integrate, is deliberately not proposed, because it introduces three problems:

  1. SSRF. Event data an attacker can influence could redirect delivery to internal or cloud-metadata endpoints (169.254.169.254, localhost, private ranges).
  2. Rate-limiting / concurrency fragmentation. Outpost caches publishers and reasons about destinations by a stable config identity. A URL that changes every event fragments that model.
  3. Fragmented telemetry. Per-destination metrics and logs assume a stable target host; a moving host makes per-destination dashboards meaningless.

Pinning scheme + host to operator-controlled config while templating only the path neutralizes all three: the host (the SSRF-relevant part) is never event-controlled, the destination identity stays stable, and telemetry stays attributed per destination.

Design choices (proposed, open to input)
  1. Separate field url_path_template rather than template markers inside url, so the base URL stays a plain, validatable URL and scheme + host can never be templated.
  2. Template inputs: metadata (and possibly data). The event's metadata string map is a small, safe surface; parsed data could also be exposed if there's appetite. One open point: metadata keys are already emitted as X-Outpost-* headers, so a value used to shape the path would also go out as a header; if that's undesirable, a reserved metadata namespace (e.g. keys prefixed _path.) could be usable in the template but filtered out of the headers.
  3. Guardrails: percent-encode resolved path segments; reject templates/results containing ://, .., @, or a leading //; enforce the rendered result is still same-origin as the configured base URL.
Open questions
  1. Template-resolution failure at delivery time — hard-fail the attempt (visible in the attempt log) vs. fall back to the base URL? Proposal: hard-fail.
  2. Where template inputs should come from — metadata only, also parsed data, or is there a different source altogether that would be a better fit than either metadata or data? Open to suggestions if neither is the right home for a path-shaping value.
主要言語
Go
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1日 18時間
マージ済み PR（30日）
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