code: def handle(cls, value, **kwargs):
          
          value = read_value_from_path(value)
  
          region = "us-east-1"
          if "@" in value:
              region, value = value.split("@", 1)
  
          client = get_session(region).client("ssm")
          response = client.get_parameters(
              Names=[
                  value,
              ],
              WithDecryption=True
          )
          if 'Parameters' in response:
              return str(response['Parameters'][0]['Value'])
  
          raise ValueError('SSMKey "{}" does not exist in region {}'.format(
              value, region))
docs: Retrieve (and decrypt if applicable) a parameter from
          AWS SSM Parameter Store.
  
          ssmstore field types should be in the following format:
  
              [<region>@]ssmkey
  
          Note: The region is optional, and defaults to us-east-1 if not given.
  
          For example:
  
              # In stacker we would reference the encrypted value like:
              conf_key: ${ssmstore us-east-1@ssmkey}
  
              You can optionally store the value in a file, ie:
  
              ssmstore_value.txt
              us-east-1@ssmkey
  
              and reference it within stacker (NOTE: the path should be relative
              to the stacker config file):
  
              conf_key: ${ssmstore file://ssmstore_value.txt}
  
              # Both of the above would resolve to
              conf_key: PASSWORD