In ASP.NET 4 this was as easy as routes.LowercaseUrls = true; in the RegisterRoutes handler for the app.
I cannot find an equivalent in ASP
For identity, @Jorge Yanes Diez answer doesn't work in ASP.NET Core 2.2 (I think 2.x), so if you use Identity and ASP.NET Core 2.2 (2.x) here is the solution:
services.ConfigureApplicationCookie(options =>
{
options.LoginPath = "/account/login";
options.ReturnUrlParameter = "returnurl";
...
});
Ref: Configure ASP.NET Core Identity