Is it possible to connect a mikrotik device on an existing network that has authentication through the browser? (hotspot). i know that i can connect but i dont know how i will authenticate through the mikrotik.
Thank you in advance.

Yes, you can.
Authentication is simply done through a client device behind that Mkrotik. Done that a couple of times and it's really straight forward.
-Chris

ok so lets say that i use a Mikrotik RouterBOARD SXT 2NDR2 and i connect on the hotspot. how i will authenticate after through the browser?it will see the interface of mikrotik not the hotspot.

to be more specific here in us the internet provider ( spectrum ) lets you have wifi from hotspot but you have to login with username and password that you enter them on the browser. I want to connect my mikrotik on this wifi and connect through this to the internet. this is possible?

you can try to use station-pseudobridge or station-pseudobridge-clone - wlan interface should be bridged, with no dhcp-client on it and hotspot should see your mac address/ip when accessing authorization...

You do not authenticate using your SXT 2NDR2. You authenticate with the PC connected behind the SXT 2NDR2.

Hotspot <--> SXT 2NDR2 <--> Several PC

So authentication is done with one of the "Several PC".
I did test this with MT using two Wifi. One connect to Hotspot and other to the PC.
MT using NAT. This way only one PC needs to authenticate, then the rest opens up.

thanks yes i think i have to bridge the wan with the lan to be honest i forgot to do this. i just connected the mt directly on the hotspot and the computer on mt but by default it was getting only local ip from mt obviously.