fix(vault): make it possible to use vault references in declarative config (#11843)

### Summary

Warmup cache on `init` where we have Lua `coroutines` available so that
it won't happen on `init_worker` where we don't have them (and cannot use
e.g. lua-resty-http).

See KAG-2620 and FTI-5080.

Signed-off-by: Aapo Talvensaari <[email protected]>

* Update spec/02-integration/02-cmd/02-start_stop_spec.lua

---------

Signed-off-by: Aapo Talvensaari <[email protected]>
Co-authored-by: Samuele <[email protected]>
(cherry picked from commit 12324a1)

Author: bungle

changelog/unreleased/kong/vault-declarative.yml

@@ -0,0 +1,3 @@
+message: Vault references can be used in Dbless mode in declarative config
+type: bugfix
+scope: Core

kong/init.lua

@@ -717,6 +717,8 @@ function Kong.init()
       if not declarative_entities then
         error(err)
       end
+
+      kong.vault.warmup(declarative_entities)
     end
 
   else

kong/pdk/vault.lua

@@ -1563,6 +1563,28 @@ local function new(self)
     init_worker()
   end
 
+  ---
+  -- Warmups vault caches from config.
+  --
+  -- @local
+  -- @function kong.vault.warmup
+  function _VAULT.warmup(input)
+    for k, v in pairs(input) do
+      local kt = type(k)
+      if kt == "table" then
+        _VAULT.warmup(k)
+      elseif kt == "string" and is_reference(k) then
+        get(k)
+      end
+      local vt = type(v)
+      if vt == "table" then
+        _VAULT.warmup(v)
+      elseif vt == "string" and is_reference(v) then
+        get(v)
+      end
+    end
+  end
+
   if get_phase() == "init" then
     init()
   end

spec/02-integration/02-cmd/02-start_stop_spec.lua

@@ -663,8 +663,43 @@ describe("kong start/stop #" .. strategy, function()
         assert.matches("in 'name': invalid value '@gobo': the only accepted ascii characters are alphanumerics or ., -, _, and ~", err, nil, true)
         assert.matches("in entry 2 of 'hosts': invalid hostname: \\\\99", err, nil, true)
       end)
-    end
 
+      it("dbless can reference secrets in declarative configuration", function()
+        local yaml_file = helpers.make_yaml_file [[
+          _format_version: "3.0"
+          _transform: true
+          plugins:
+          - name: session
+            instance_name: session
+            config:
+              secret: "{vault://mocksocket/test}"
+        ]]
+
+        finally(function()
+          os.remove(yaml_file)
+        end)
+
+        helpers.setenv("KONG_LUA_PATH_OVERRIDE", "./spec/fixtures/custom_vaults/?.lua;./spec/fixtures/custom_vaults/?/init.lua;;")
+        helpers.get_db_utils(strategy, {
+          "vaults",
+        }, {
+          "session"
+        }, {
+          "mocksocket"
+        })
+
+        local ok, err = helpers.start_kong({
+          database = "off",
+          declarative_config = yaml_file,
+          vaults = "mocksocket",
+          plugins = "session"
+        })
+
+        assert.truthy(ok)
+        assert.not_matches("error", err)
+        assert.logfile().has.no.line("[error]", true, 0)
+      end)
+    end
   end)
 
   describe("deprecated properties", function()

spec/fixtures/custom_vaults/kong/vaults/mocksocket/init.lua

@@ -0,0 +1,37 @@
+local env = require "kong.vaults.env"
+local http = require "resty.luasocket.http"
+
+
+local assert = assert
+local getenv = os.getenv
+
+
+local function init()
+  env.init()
+  assert(getenv("KONG_PROCESS_SECRETS") == nil, "KONG_PROCESS_SECRETS environment variable found")
+  assert(env.get({}, "KONG_PROCESS_SECRETS") == nil, "KONG_PROCESS_SECRETS environment variable found")
+end
+
+
+local function get(conf, resource, version)
+  local client, err = http.new()
+  if not client then
+    return nil, err
+  end
+
+  client:set_timeouts(20000, 20000, 20000)
+  assert(client:request_uri("http://mockbin.org/headers", {
+    headers = {
+      Accept = "application/json",
+    },
+  }))
+
+  return env.get(conf, resource, version)
+end
+
+
+return {
+  VERSION = "1.0.0",
+  init = init,
+  get = get,
+}

spec/fixtures/custom_vaults/kong/vaults/mocksocket/schema.lua

@@ -0,0 +1,13 @@
+return {
+  name = "mocksocket",
+  fields = {
+    {
+      config = {
+        type = "record",
+        fields = {
+          { prefix = { type = "string", match = [[^[%a_][%a%d_]*$]] } },
+        },
+      },
+    },
+  },
+}