When setting up Wordpress on a local Mac OSX server using this great guide (which also applies to Mavericks):-http://mactasia.co.uk/lion-server-mysql-and-wordpress... we encountered the following issue when trying to edit the server php.ini file:-

The authenticated save for this file failed (application error code: 20004)

The reason for this is actually due to ownership and permission sod the file which OSX Server locks down. To get Wordpress running on a local server you do need to edit and control this file and the solution is actually very easy. You simply need to update the editor (in our case TextWrangler) to the full version that permits 'authenticated saves'. Here is the reason from Bare Bones Software:-"Authenticated saves are not possible in versions of TextWrangler obtained from the Mac App Store. If you desire this capability, please download TextWrangler directly from us."

So, you require the full download version of TextWrangler to write to files that require authentication / that you don't own.

TextWrangler is now part of BBEdit.

Please note that Bare Bones Software have sunsetted TextWrangler, and BBEdit has changed to make room for TextWrangler users. You can use BBEdit instead; it’s still free to use the same set of features that TextWrangler provided.