I'm building a WebServices tha allows user from a social network to add a new FILE in a DoCLibrary. This WebServices' WSDl ,was built with no "USERID" field . Every time that someone add a new file on sharepoint, it's created as "SHAREPOINT/SYSTEM" author. So, every Domain user has his own account on sharepoint that is the same on the web site social network. I need to knows how can I get the user instance that is logged on the WebSite , that is adding a new file on SP, to modify that "FILE AUTHOR"field on sharepoint ?
You can create a textbox set it to read only and in the default value settings feild under properties, you can add a function in this case UserName() which will pull from active directory.
I hope this is what you were looking for.