Server Side Code?

I'm having a little trouble understanding where I put the server-side code for Photon. All of the tutorials seem to be based around the premise that the clients do all the work and data is sent to the server and is then 'echoed' to all the other clients.

Is this correct? Is there no server-side validation of the data at all?

I'm also using PlayFab, which has server-side code, but the code isn't 'tied' to any particular game. My understanding of combining these two products is that Photon handles the local game information (IE - the actual location of the pieces and how many hit points units have etc) and passes requests to Playfab when it needs to check specific TitleData queries or broad code access.

However, it feels like Photon is literally just an echo chamber - I can't actually code on it. Which means I'm relying on my clients to handle the majority of my game logic, which does not seem like good practice. Also it makes me wonder why use Photon at all at that point, since everything is basically handled by Unity and PlayFab.

Can someone point me in the right direction? Surely there's some Photon Server Side documentation somewhere that I'm missing.