To add PHP extensions to your Azure web site:
1) Create a folder named bin within your site/wwwroot folder
2) Download the appropriate PHP extension (http://php.net) for the version of PHP you are running on your site. You want to download the 'vc9-nts' version. Rename the file without the vc9-nts in the name.
3) Upload the .dll file you renamed above to the bin folder you created.
4) From the "Configure" area of your web management portal, create an App Settings entry. In the KEY field put PHP_EXTENTIONS, and in the VALUE field enter the path to the DLL file. For example:
(if you need to enable multiple PHP extensions, separate the DLL values with commas)
To confirm that the extension is now active in PHP you can upload a php test page that contains the following code: