How you handle many apis in you app

Hey, I am Yassin I am a Web dev actually using Nextjs I was Getting a problem and it is that I don't know how to manage my Apis and secure the keys and I don't actually want to deal with Sdks so I am building KeySphere which is a simple app that let you choose a provider and add you Api key then you Api key is encrypted and is secured and you just can call any of you provider by an endpoint that does not require a Api key it is just an endpoint that gets your cookies that are HTTPonly so no JavaScript can access it so it is secured you just pass Json and it works I am open and will appreciate any feedback