Why is <deny users=“?” /> included in the following example?

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

Answer 2

"At run time, the authorization module iterates through the allow and deny elements, starting at the most local configuration file, until the authorization module finds the first access rule that fits a particular user account. Then, the authorization module grants or denies access to a URL resource depending on whether the first access rule found is an allow or a deny rule. The default authorization rule is . Thus, by default, access is allowed unless configured otherwise."

Article at MSDN

deny = * means deny everyone
deny = ? means deny unauthenticated users

In your 1st example deny * will not affect dan, matthew since they were already allowed by the preceding rule.

According to the docs, here is no difference in your 2 rule sets.

Answer 3

Example 1 is for asp.net applications using forms authenication. This is common practice for internet applications because user is unauthenticated until it is authentcation against some security module.

Example 2 is for asp.net application using windows authenication. Windows Authentication uses Active Directory to authenticate users. The will prevent access to your application. I use this feature on intranet applications.

Answer 4

See this two links:

deny Element for authorization (ASP.NET Settings Schema) http://msdn.microsoft.com/en-us/library/vstudio/8aeskccd%28v=vs.100%29.aspx

allow Element for authorization (ASP.NET Settings Schema): http://msdn.microsoft.com/en-us/library/vstudio/acsd09b0%28v=vs.100%29.aspx