AuthController.cs

private async Task LoginAsync(User user)
{
    var claims = new List<Claim>
    {
        new Claim(ClaimTypes.NameIdentifier, user.UserName),
        new Claim(ClaimTypes.Name, user.UserName),
        new Claim(ClaimTypes.GivenName, user.FirstName),
        new Claim(ClaimTypes.Surname, user.Surname),
        new Claim(ClaimTypes.Email, user.Email, ClaimValueTypes.Email),
        new Claim(ClaimTypes.DateOfBirth, user.DateOfBirth.ToString("O"), ClaimValueTypes.Date)
    };
    var identity = new ClaimsIdentity(claims, CookieAuthenticationDefaults.AuthenticationScheme);
    var principal = new ClaimsPrincipal(identity);
    await HttpContext.SignInAsync(principal);
}