Where I can save my openai-apikey safely for my flutter app

I am trying using ability of openai for my flutter app, but for now I don’t have experience to save apikey safely and efficiently etc. I learned that I can save my openai apikey somewhere in the firebase and let flutter client visit the firebase to get the access to openai.

But for now I do not know the total correct process or code example to handle this issue, could someone share some article or some existing method between flutter and firebase for saving apikey saving? It could be great to share the dis-and-advantage for costs or time-consuming.

Thanks a lot!