'Filter access to describe_stack_resource for in-instance users.
- The user must map to a User resource defined in the requested stack
- The user resource must validate OK against any Policy specified'

def _authorize_stack_user(self, cnxt, stack, resource_name):

    if stack.access_allowed(cnxt.user_id, resource_name):
        return True
    try:
        ec2_creds = jsonutils.loads(cnxt.aws_creds).get('ec2Credentials')
    except (TypeError, AttributeError):
        ec2_creds = None
    if (not ec2_creds):
        return False
    access_key = ec2_creds.get('access')
    return stack.access_allowed(access_key, resource_name)
