Signing into App Store automatically allows accessing iCloud?

I did a wrong thing today, one of my friends asked me to help sign in my Apple id into his iPhone's App Store to download an App, so I helped him with that. I shouldn't do that, but I thought it should be fine since it's just the App Store. However, later today, I experimented on my own iPhone, and I realized that, by signing into the App Store, there will be no further authentication steps required for the device to sign in to the iCloud with the same Apple id. Is this expected? Since I thought logging into App Store should not allow access to iCloud. Can Apple fix this? (I know I did a wrong thing, but I was just too willing to help at that very moment). What I am expecting was, even with App Store signed in, if you want to sign in to iCloud, you still need to go through all the authentication steps required.