ASP.net Razor page - C# code behind log in button

Can you post your html code?
Try to find some code like this:

<button type="submit" 

Select allOpen in new window

or

 <input type="submit" value="Login" asp-page-handler="LoginHandler" />

Select allOpen in new window

LoginHandler method in your controller can handle button click event on server

Can you post the sample of your cshtml desgin. Ideally if you see like this

using (Html.BeginForm("ActioName", "ControllerName", FormMethod.Post))
{
}

Select allOpen in new window

Then your code will be in respective controller, in your example it might be in AccountController check for post method and see