Question

The ? wildcard represents unauthenticated users while * represents all users, authenticated and unauthenticated. My book shows the following example of URL authorization:

<authorization>
  <deny users="?" />
  <allow users="dan,matthew" />
  <deny users="*" />
</authorization>

But doesn’t the above code have the same effect as :

<authorization>
  <allow users="dan,matthew" />
  <deny users="*" />
</authorization>

or did the author also include <deny users="?" /> rule for a reason?

Answer 1

ASP.NET grants access from the configuration file as a matter of precedence. In case of a potential conflict, the first occurring grant takes precedence. So,

deny user="?" 

denies access to the anonymous user. Then

allow users="dan,matthew" 

grants access to that user. Finally, it denies access to everyone. This shakes out as everyone except dan,matthew is denied access.

Edited to add: and as @Deviant points out, denying access to unauthenticated is pointless, since the last entry includes unauthenticated as well. A good blog entry discussing this topic can be found at: Guru Sarkar’s Blog