title: Failure to invoke Lambda cross-account for creating a Lambda-backed custom resource
body: <p>I'm trying to implement a use case, where a Lambda function can be invoked across-account through an <em>AWS CloudFormation</em> template.</p>
  
  <p>I'm deploying an <em>AWS CloudFormation</em> stack in <code>account B</code>, which has a custom resource that invokes that Lambda function defined in <code>account A</code>.
  I have created a cross account role for Lambda in <code>account A</code> with <code>account B</code> as a trusted entity. Also, the user in <code>account B</code> has been attached with a policy that allows it to assume this role.
  Unfortunately, the stack creation fails the access error.</p>
  
  <p>Would appreciate any help. Here's my template for <em>account B</em>:</p>
  
  <pre><code>{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Resources": {
      "GetNwInterfaces":{
        "Type": "Custom::GetNwInterfaces",
        "Properties": {
          "ServiceToken": "arn:aws:lambda:ap-northeast-2:XXXXXXXXXX:function:getini2",
          "region": "us-west-2",
          "uid" : "01100"
        }
      }
    }
  }
  </code></pre>