Send Application plan as a header named X-3scale-Plan

nginx.conf

...
    location / {
      set $provider_key null;
      set $cached_key null;
      set $credentials null;
      set $usage null;
      set $service_id YOURSERVICEID;
      set $proxy_pass null;
      set $secret_token null; 
      set $plan_header null; # ADD THIS LINE

      proxy_ignore_client_abort on;

      ## CHANGE THE PATH TO POINT TO THE RIGHT FILE ON YOUR FILESYSTEM
      access_by_lua_file /opt/openresty/nginx/conf/nginx.lua;

      proxy_pass $proxy_pass ;
      proxy_set_header  X-Real-IP  $remote_addr;
      proxy_set_header  Host  api-sentiment.3scale.net;
      proxy_set_header X-3scale-proxy-secret-token $secret_token;
      proxy_set_header X-3scale-plan $plan_header; # ADD THIS LINE

      post_action /out_of_band_authrep_action;
    }
...

nginx.lua

-- new helper function to add
function parse_cached_value(val)
  local is_known, plan
  if val == nil then
    is_known = false
    plan = nil
  else
    local idx = val:find(":")
    if idx then
      is_known = val:sub(1, idx-1)
      plan = val:sub(idx+1)
    else
      is_known = val
      plan = nil
    end
  end
  return is_known, plan
end

-- replace authrep function by this one
function authrep(params, service)
  ngx.var.cached_key = ngx.var.cached_key .. ":" .. ngx.var.usage
  local api_keys = ngx.shared.api_keys

  local val = api_keys:get(ngx.var.cached_key)
  local is_known, cached_plan = parse_cached_value(val)
  -- set X-3scale-Plan header if it was in the cache before
  -- otherwise will be nil and will be overwritten below
  ngx.var.plan_header = cached_plan


  -- key is not in cache, check synchronously with 3scale backend
  if is_known ~= "200" then
    local res = ngx.location.capture("/threescale_authrep", { share_all_vars = true })
    -- get Application plan
    local m, err = ngx.re.match(res.body, [[<plan>(\w+)<\/plan>]])
    local plan
    if m then plan = m[1] end

    if res.status ~= 200 then
      -- not authorized, make sure we delete the key from cache
      api_keys:delete(ngx.var.cached_key)
      -- unset X-3scale-Plan
      ngx.var.plan_header = nil
      ngx.status = res.status
      ngx.header.content_type = "application/json"
      error_authorization_failed(service)
    else
      -- authorized, cache key to check asynchronously on next request
      local cached_value = "200:" .. plan
      -- keep Application plan in the local cache for next requests
      api_keys:set(ngx.var.cached_key, cached_value)
      -- set header X-3scale-Plan
      ngx.var.plan_header = plan
    end
    ngx.var.cached_key = nil
  end
end