RFC: add preunpack life cycle script

accepted/0000-add-preunpack-life-cycle-script.md

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+# RFC: Add `preunpack` life cycle script
+
+## Summary
+
+Add a `preunpack` life cycle script that runs before anything else.
+
+## Motivation
+
+npm v7 introduced a new order of running the `preinstall` script, where it runs **after** dependencies are installed, breaking backward compatibility with packages expecting to run a script **before** dependencies are installed.
+
+By introducing a new life cycle script that will run first in the execution order, we can give a path forward to packages that require a script to run **before** dependencies are installed.
+
+Use cases:
+
+* Handling authentication for private registries with short-lived tokens (i.e., AWS, GCP, Azure)
+* Generating workspaces from gRPC proto files before workspaces and dependencies get evaluated.
+
+## Detailed Explanation
+
+A `preunpack` life cycle script that is **first** in execution order:
+
+* Runs on local `npm install` without any arguments
+* Runs on non-local `npm install` (from a package being unpacked)
+* Runs on `npm ci`
+
+Example usage in the case of handling authentication for AWS CodeArtifact:
+
+```json
+{
+  "name": "my-app",
+  "version": "1.0.0",
+  "description": "A sample application consuming a private scoped npm package",
+  "main": "index.js",
+  "scripts": {
+    "preunpack": "npm run co:login",
+    "co:login": "aws codeartifact login --tool npm --repository my-repo --domain my-domain"
+  },
+  "dependencies": {
+    "@myorg/my-package": "^1.0.0"
+  }
+}
+```
+
+When running `npm install`, the `npm run co:login` will be run before any dependencies are installed.
+
+## Rationale and Alternatives
+
+### Implement a separate top level "events" field
+
+The idea here would be to implement a top-level "events" field to keep the current behavior of "scripts" while providing a better implementation elsewhere as described in [this comment](https://github.com/npm/cli/issues/2660#issuecomment-794415767).
+
+This approach would undoubtedly address the use cases outlined above, but the scope may be too large when we need a quicker stop-gap for the interim.
+
+### Revert back to the `preinstall` functionality from versions before v7
+
+See [Unresolved Questions and Bikeshedding](#unresolved-questions-and-bikeshedding).
+
+## Implementation
+
+<!-- Give a high-level overview of implementation requirements and concerns. Be specific about areas of code that need to change, and what their potential effects are. Discuss which repositories and sub-components will be affected, and what its overall code effect might be. -->
+
+<!-- THIS SECTION IS REQUIRED FOR RATIFICATION -- you can skip it if you don't know the technical details when first submitting the proposal, but it must be there before it's accepted -->
+
+## Prior Art
+
+* npm v6
+
+## Unresolved Questions and Bikeshedding
+
+* Are there any security implications with this approach?
+* Are we sure we don't want to revert back to the `preinstall` functionality of npm v6?
+
+<!-- THIS SECTION SHOULD BE REMOVED BEFORE RATIFICATION -->