So I have a hAP ac lite, but when I enter with winbox and look at the html files of the hotspot, they are not the original ones, apparently someone already used this AP to upload their files.

So I factory reset the AP, but that only affects the configuration.

My first question is, if I flash the AP OS, will the original hotspot files be loaded? That is to say those of mikrotik?

I want to make a hotspot and have the mikrotik files as a base.

I would like to make a common facebook login, but I suppose that for that I have to work with the facebook api, right? I have already realized that you have to allow the connection to facebook through walled warden.

Another example, that the user obtain the credentials to access the hotspot by pressing a button, for example could he create only one user and pass, and make an <input> with that name and username for all hotspot clients?

They would be reflected as different users, by MAC or something like that, but when they all start, they start with the same user and pass stored in the html code.

I don't know if it's better to do it with a Cookie MAC.

Another question would be to create an SSL certificate, for a secure connection, since the network is open.

Thanks.

To be on the safe side, use NETINSTALL to upload the latest stable software recommend long term 6.48 version.
If you want to use wireguard then you will need V7 firmware and the latest stable version of that.

MT doc - https://help.mikrotik.com/docs/display/ROS/Netinstall
Tips See Para H. here --> viewtopic.php?t=182373 .

within winbox you can reset to default mikrotik hotspot html page with this button...

Thanks guys, I'll try the other points by myself. I was able to restore the html, to have a good base.