Shared SSM parameters don't seem to be working

[iiroj]

Describe the bug

SSM parameters shared between AWS accounts don't seem to be working in with the Middy.js ssm middleware. See more info about the feature here: https://docs.aws.amazon.com/systems-manager/latest/userguide/parameter-store-shared-parameters.html

Since the shared parameter needs to be fetched with the Name being the full ARN of the parameter like arn:aws:ssm:us-east-1:000000000000:parameter/foo, the fetched value seems to be lost somewhere inside the Middy.js cache, given that the Name returned in the SSM response is only the path /foo (in the other AWS account). Thus, I believe the issue is somewhere here:

middy/packages/ssm/index.js

Lines 105 to 109 in e657041

	for (const internalKey of batchInternalKeys) {
	values[internalKey] = batchReq.then((params) => {
	return params[options.fetchData[internalKey]];
	});
	}

where options.fetchData[internalKey]] refers to the full ARN arn:aws:ssm:us-east-1:000000000000:parameter/foo, but in params the value exists only with the parm path /foo.

middy/packages/ssm/index.js

Lines 93 to 95 in e657041

	...(resp.Parameters ?? []).map((param) => {
	return { [param.Name]: parseValue(param) };
	}),

To Reproduce

Use the ssm middleware to get a shared parameter from another aws account:

ssm({
  fetchData: {
    foo: 'arn:aws:ssm:us-east-1:000000000000:parameter/foo'
  },
  setToContext: true
})

And try to access context.foo, which will be undefined.

Expected behaviour
A clear and concise description of what you expected to happen.

Environment (please complete the following information):

• Node.js: 22.x (Lambda runtime
• Middy: tested with 5.5.1 and 6.4.5
• AWS SDK tested with 3.799.0

Additional context
Add any other context about the problem here.

[iiroj]

I added a Draft PR with an unit test showing the failure scenario.

[iiroj]

I also took the liberty of adding one possible fix to the linked PR, but I'm not sure it's the most optimal solution!