feat: Add legacy createOriginMiddleware (#8734)

## Explanation

Recently we added `createOriginMiddleware` to `v2` for usage in the
clients. Though using it via `asLegacyMiddleware` introduces some
complications, so for the time being we introduce the same middleware
using the legacy API.

## References

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* Fixes #12345
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## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk additive change: introduces a new legacy middleware and
export without altering existing middleware behavior, with a small
chance of conflicts for consumers that already attach an `origin` field
to requests.
> 
> **Overview**
> Adds a legacy `createOriginMiddleware` for `@metamask/json-rpc-engine`
that mutates the JSON-RPC request object to include an `origin` string
(marked *deprecated* in favor of the v2 API).
> 
> Exports the new utility from the package entrypoint, updates export
snapshot tests, adds a unit test verifying `origin` is set, and records
the addition in the package changelog.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
710f931. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: FrederikBolding

packages/json-rpc-engine/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add legacy `createOriginMiddleware` utility ([#8734](https://github.com/MetaMask/core/pull/8734))
+
 ## [10.3.0]
 
 ### Added

packages/json-rpc-engine/src/createOriginMiddleware.test.ts

@@ -0,0 +1,27 @@
+import { JsonRpcRequest } from '@metamask/utils';
+
+import { makeRequest } from '../tests/utils';
+import { createOriginMiddleware } from './createOriginMiddleware';
+import { JsonRpcEngine } from './JsonRpcEngine';
+
+describe('createOriginMiddleware', () => {
+  it('adds the origin property to the request', async () => {
+    const origin = 'https://metamask.io';
+    const engine = new JsonRpcEngine();
+
+    engine.push(createOriginMiddleware(origin));
+
+    engine.push((request, response, _next, end) => {
+      response.result = (
+        request as unknown as JsonRpcRequest & { origin: string }
+      ).origin;
+      end();
+    });
+
+    expect(await engine.handle(makeRequest())).toStrictEqual({
+      id: '1',
+      jsonrpc: '2.0',
+      result: origin,
+    });
+  });
+});

packages/json-rpc-engine/src/createOriginMiddleware.ts

@@ -0,0 +1,19 @@
+import { Json, JsonRpcRequest } from '@metamask/utils';
+
+import { JsonRpcMiddleware } from './JsonRpcEngine';
+
+/**
+ * Create a middleware function that adds `origin` to the request object.
+ *
+ * @deprecated Use the v2 `createOriginMiddleware` instead.
+ * @param origin - The origin.
+ * @returns The middleware.
+ */
+export function createOriginMiddleware(
+  origin: string,
+): JsonRpcMiddleware<JsonRpcRequest, Json> {
+  return (request, _result, next) => {
+    (request as unknown as JsonRpcRequest & { origin: string }).origin = origin;
+    next();
+  };
+}

packages/json-rpc-engine/src/index.test.ts

@@ -7,6 +7,7 @@ describe('@metamask/json-rpc-engine', () => {
         "asV2Middleware",
         "createAsyncMiddleware",
         "createMethodMiddleware",
+        "createOriginMiddleware",
         "createScaffoldMiddleware",
         "getUniqueId",
         "createIdRemapMiddleware",

packages/json-rpc-engine/src/index.ts

@@ -10,6 +10,7 @@ export type {
   MethodHandlerImplementation,
 } from './createMethodMiddleware';
 export { createMethodMiddleware } from './createMethodMiddleware';
+export { createOriginMiddleware } from './createOriginMiddleware';
 export { createScaffoldMiddleware } from './createScaffoldMiddleware';
 export { getUniqueId } from './getUniqueId';
 export { createIdRemapMiddleware } from './idRemapMiddleware';