title: On Which Tier should user authentication should exist in n-tier website
body: <p>I went through different Architecture books such as this one: <a href="https://msdn.microsoft.com/en-us/library/ff650706.aspx?f=255&amp;MSPPError=-2147217396" rel="nofollow">Microsoft Application Architecture Guide, 2nd Edition</a> 
  And now I am building a new n-tier website with ASP.Net MVC as Presentation layer.
  My question is, If I will use the <a href="http://www.asp.net/identity" rel="nofollow">asp.net Identity</a>, on which tier/layer should I implement the user authentication?</p>
  
  <p>I thought it should be in the Cross Cutting Concerns, because I will need to check if user is authorized or authenticated to access some functions plus I may use the user name on many tiers, such as the Business, Services and Presentation layer.</p>
  
  <p>and also thought it will be better to put it in the Presentation layer specially because the presentation layer is MVC and it will be easy to deal with ASP Identity from there and will allow me to user [Authorize] and [AllowAnonymous] easily.</p>
  
  <p>I know that this question answer depend on many other factors but I am trying here to achieve the most best practice, so need to get your point of view and discuss it.</p>