RFC: Add configurable data to HTTP header

accepted/0027-additional-http-header-values.md

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+# Send additional HTTP header information as defined in a list of `header` items in .npmrc
+
+## Summary
+
+HTTP header may contain additional `header` information which may be used in third-party applications.
+
+## Motivation
+
+Third-party applications may enhance decisions made based on the extra information to provided, such as individualised audits
+
+## Detailed Explanation
+
+Developers and users who are integrated with third-party tooling will have the opportunity surface additional and project focused information when using commands such as `npm audit`.
+
+Currently, for developers who perform `npm audit` or `npm install` integrated with third-party applications there is no way to provide additional information.
+Like `npm-session` is used by the npm registry to identify individual user sessions, it would be useful to provide a generic way for a maintainer to add additional metadata to their project which is sent during an `npm audit` or `npm install` (but not limited to).
+
+## Rationale and Alternatives
+
+* **Rationale:** 
+  * This is easy to implement solution to provide such additional value in the HTTP request.
+  * Building this functionality will allow developers to easily set additional information that can be passed along in a header for third-party applications to use
+
+* **Alternatives:** 
+  * Use `preshrinkwrap` or/and `postshrinkwrap` scripts to install a custom value to the project.
+
+## Implementation
+
+* Define a new `header` configuration item that can be added to either the global or project .npmrc file.
+* The list of `header` values will be converted to a single JSON object and picked up by the [npm cli](https://github.com/npm/cli) and sent as a `header` attribute in the HTTP header requests
+
+An illustrative `.npmrc` example:
+
+```
+; project-level .npmrc
+headers[]="npm-app-id: a config value"
+headers[]="Authorization: some customized authorization information"
+```
+
+### Additional configuration
+It should also be possible to define additional headers to be appended or overwritten from the command line.
+
+An illustrative example:
+`npm audit --headers="npm-app-id: value"`
+
+In this example, the HTTP header would override the `.npmrc` provided value for `npm-app-id` with the value provided from the command line.
+
+## Prior Art