AppSync HTTP resolver - StartSyncExecution for StepFunctions express workflows

Data Source.json

{
  "apiId": "xxxxxxxxxxxxxxxxxxxxxxxxxx",
  "name": "sync_step_function",
  "description": "step function test",
  "type": "HTTP",
  "serviceRoleArn": "arn:aws:iam::xxxxxxx:role/appsync-step-function",
  "httpConfig": {
    "endpoint": "https://sync-states.us-east-2.amazonaws.com",
    "authorizationConfig": {
      "authorizationType": "AWS_IAM",
      "awsIamConfig": {
        "signingRegion": "us-east-2",
        "signingServiceName": "states"
      }
    }
  }
}

Request.json

{
  "version": "2018-05-29",
  "method": "POST",
  "resourcePath": "/",
  "params":{
      "headers": {
          "content-type": "application/x-amz-json-1.0",
          "x-amz-target": "AWSStepFunctions.StartSyncExecution"
      },
      "body": {
      	"stateMachineArn": "arn:aws:states:us-east-2:xxxxxxxxx:stateMachine:xxxxxxxx",
        "name": "xxxxxx"
      }
  }
}