IIS: redirect to a webpage if authentication fails
Solution 1:
We managed to figure this out.
In IIS 7.0 the following changes need to be made to get custom HTML error pages to display:
Add the following to the Applications web.config after
<system.webServer>
<httpErrors errorMode="Custom" existingResponse="Auto" >
</httpErrors>
</system.webServer>
Then run the command "appcmd unlock config -section:httpErrors" to stop IIS giving a 500 error from these changes