Unable to enable the vSphere Authentication Proxy Plug-in

I recently had some issues getting the vSphere Authentication Proxy Plug-in to be enabled within vCenter Server 5.1. This is the error message that was displayed: “The server could not interpret the client’s request. (The remote server returned an error: (404) Not Found.)” 

After extensive troubleshooting it appears that the following has happened:

• The Auto Deploy Software is installed on a clean Windows 2008 R2 SP1 system;
• When you try to install the Microsoft .NET 3.5 SP1 from the Autorun screen you will get a message that this needs to be installed via the Role Management Tool;

• Installing Microsoft .NET 3.5 SP1 via the Role Management Tool also installed some IIS Components (all wizards are kept default) as shown on the screenshot below;

• The installation of the vSphere Authentication Proxy now gives a message that it requires additional IIS components (IIS 6 Metabase Compatibility, ISAPI Extensions, IP and Domain Restrictions) as shown on the screenshot below;

• So consequently I install the missing IIS Components via the Role Management Tool;
• After successful installation of the vSphere Authentication Proxy you will now experience that the plug-in cannot be enabled within vCenter as described in the beginning of this article.

The reason why the vCenter Server cannot enable the plug-in is due to the fact that the extension.xml cannot be accessed. This problem is caused by the incomplete installation of IIS. To resolve this situation follow the steps below:

• Install Static Content, Default Document, Directory Browsing and HTTP Errors as additional components to IIS via the Role Management Tool;

• Now enable the vSphere Authentication Proxy from vCenter.

Root cause
The four additional IIS components  that needed to be installed are default to IIS whenever you cleanly add the Web Server role via the Role Management Tool. However, since the installation of .NET3.5 installed some IIS components the vSphere Authentication Proxy installation did not show the message below which requests for IIS and basically assumes that IIS is installed correctly (which it was not)