How to custom the response body for JWT and rate-limiting plugin?

[XJShane]

Hi i want to custom the response body when JWT or rate-limiting plugin return, to compatible with older programs, for example:
{
"status": 401,
"msg": "token expired"
}

{
"status": 429,
"msg": "rate limit exceed"
}

kong version: 2.2.0

I'm not sure that modifying the source code for JWT and rate-limiting plugin is a good idea, if there's no other way.

[tyree731]

These plugins run in Kong/openresty's access phase, meaning that after they call kong.response.exit, you should be able to customize the returned response by running a custom plugin with an appropriate header_filter and body_filter phase.

[XJShane]

Hi @tyree731 i also need to get the response data for JWT plugin returned, i have already write a custom plugin, but after the JWT plugin, the access phase in custom plugin not executed, but the response data only can get in this phase. I think the reason is that JWT access phase has called kong.response.exit, when the priority less than JWT plugin, it dont't executed the access phase anymore.

[tyree731]

When you say "the response data for JWT plugin", do you mean the above referenced response body:

{
  "status": 401,
  "msg": "token expired"
}

If so, that body will be available if your plugin operates in the body_filter or response plugin phases. Perhaps an example would help? We have a custom plugin that authorizes users based on whether they have access to a given service. If the user does not have access, we run code that looks something like like:

local forbidden_response = function(response_message)
  return kong.response.exit(403, response_message, {["Content-Type"] = "text/plain"})
end

Separately we have a plugin that, when being requested from our websites, templates plaintext responses from downstream services to make those responses match our company's design guidelines. That plugin has a header_filter phase which checks to see if we will be templating the response, a check which uses request information and the response "Content-Type" header. If we will be templating the response, the header_filter portion of the plugin clears the response "Content-Length" header, sets an appropriate "Content-Type" header on the response, and sets a request context variable which indicates that the body_filter phase should run. In the body_filter phase we buffer the entire response body and, once that buffering is complete, we template the response body and send it out.

This response template plugin works on the body set by the kong.response.exit call. You should be able to do something similar for your example.