How to Use External Lua Scripts with the `pre-function` Plugin in declarative config

How can I reference an external Lua script file, such as function.lua, in the config.access field of the pre-function plugin when using Kong with declarative configuration files and Deck CLI?

While Kong DecK does not support referencing external files directly, you can achieve your goal by using environment variables to include the content of your Lua script. Here’s how you can do it:

1. Create your Lua script and save it in a file, for example, function.lua.

2. Load the content of the Lua script into an environment variable using the following command:

   export DECK_FUNCTION=$(cat function.lua)

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3. Reference the content of the environment variable in your declarative configuration file. Since Kong Deck v1.22.0, you can use indentation to include multiline variable content. Here’s an example of how to do this in your configuration:

   plugins:
   - config:
       access:
       - |
         ${{ env "DECK_FUNCTION" | indent 8 }}
     enabled: true
     name: pre-function

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This approach allows you to maintain the readability and maintainability of your configurations, especially when dealing with complex Lua scripts.