Nginx+Lua+s3文件上传

我正在尝试使用nginx和Lua将文件上传到s3存储桶，在此过程中我有一个sha256函数，该函数在nginx.conf之外的其他文件中当我尝试访问该函数时，我会得到以下错误。[输入图像说明文字][1]请解释一下？

'''2021/06/08 23:21:04 [error] 10480#0: *1 failed to run set_by_lua*: set_by_lua:1: attempt to index global 'sha256' (a nil value)'''

下面是我的nginx.conf

      set_by_lua $date "return ngx.http_time(ngx.time())";
      set_sha1 $datesha $date;
      set $upload_id $prefixsha$datesha;
      set $key $entity/$property/$upload_id/original/$filename;
      set $bucket "raviuploadbucket";
      #set $url http://$bucket.s3.us-east-2.amazonaws.com/$key;
      set $url http://raviuploadbucket.s3.us-east-2.amazonaws.com/upload;
      set $aws_access_key "AAAAAAAAAAAAAAAAAA";
      set $aws_secret_key "XXXXXXXXXXXXXXXXXXXX";
      set $acl public-read;
      set $canonicalized_amz_headers "x-amz-acl:$acl\nx-amz-date:$date";
      set $canonicalized_resource "/$bucket/$key";
      set $string_to_sign "$request_method\n$http_content_md5\n$http_content_type\n\n$canonicalized_amz_headers\n$canonicalized_resource";
      set $digest "sha256.hmac_sha256($aws_secret_key,$string_to_sign)";

      set $aws_region us-east-2;
      set $aws_role iam;
      set $aws_req aws4_request;

      #local k_date = sha256.hmac_sha256('AWS4' .. $aws_secret_key, $date);
      #ngx.req.set_header('k_date', sha256.hmac_sha256('AWS4' .. $aws_secret_key, $date));

      set_by_lua $k_date "return sha256.hmac_sha256('AWS4' .."XXXXXXXXXXXXXXXXXXXX", "20210608")";
      set_by_lua $k_region "return sha256.hmac_sha256($k_date, "us-east-2")";
      set_by_lua $k_service "return sha256.hmac_sha256($k_region, "iam")";
      set_by_lua $k_signing "return sha256.hmac_sha256($k_service, "aws4_request")";
      set_by_lua $signature "return sha256.hmac_sha256($k_signing, $string_to_sign))";

set $aws_signature ngx.encode_base64($digest);

      #proxy_set_header Authorization "AWS $aws_access_key:$aws_signature";
      proxy_set_header Authorization "$signature";
      proxy_set_header x-amz-acl $acl;
      proxy_set_header Date $date;
      #proxy_set_header x-amz-date: 1622471175;
      proxy_hide_header x-amz-id-2;
      proxy_hide_header x-amz-request-id;
      add_header X-File-URL $url;
      #ngx.log(proxy_set_header)
      proxy_read_timeout 300s;
      proxy_connect_timeout 75s;
      resolver 8.8.8.8 valid=300s;
      resolver_timeout 10s;
      #proxy_set_header X-Forwarded-For $
      proxy_pass $url;
    }
  }
}'''


**"下面的图片是支持AWS V4 sha256的sha256.lua文件，该文件在nginx文件夹中"**我正在尝试在nginx.conf文件中调用下面的函数创建aws签名不确定我做错了什么，任何指针都将非常赞赏。

  [1]: https://i.stack.imgur.com/6UixV.png