Getting rid of Sharepoint Site HTTP 403 Error - Forbidden or Access Denied error

Recently in our sharepoint web application i encountered HTTP 403 error for one of our web page. The strange thing about this error was that nature of the error was intermittent. i.e. sometimes user was able to view the page but sometimes users were receiving 403 response from web server.

The problem was further complicated by the fact that users were able to access the page once any admin users log in and access the page. after sometime, they were used to complain about 403 error.
If i reset the IIS or restart the server, once again all users were started receiving 403 error again. So something was terribly wrong!!!

We had Ajax enabled custom sharepoint smart part(webpart with user control) on the page and when i have removed the part from page everything was working fine. But, that's not the solution. But, one thing i could conclude that something is wrong with the webpart. But what, let us investigate!!!
(Webpart debugging in sharepoint becomes complex when Ajax and user controls are part of it.)

In my case the response was following:



but it can be in nay of following form:

1.

You are not authorized to view this page
You do not have permission to view this directory or page using the credentials that you supplied.
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2.

Please try the following:

Contact the Web site administrator if you believe you should be able to view this directory or page.
Click the Refresh button to try again with different credentials.
HTTP Error 403 - Forbidden: Access is denied.
Internet Information Services (IIS)

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3.
Technical Information (for support personnel)

Go to Microsoft Product Support Services and perform a title search for the words HTTP and 403.
Open IIS Help, which is accessible in IIS Manager (inetmgr), and search for topics titled About Security, Authentication, and About Custom Error Messages.

Solution:

As the error message clearly indicates that you are not authorized to access some resource. It could be page itself, image, css, xml files, web service files(.asmx files), assembly(yes, assembly!!!) , resource Assembly(satellite assembly) or any other resource you can think of.

I started debugging with HTTP error logs and IIS logs in order to identify the resource forwhich HTTP 403 was thrown.

1. First i found that the users are getting 403 errors for some XML files that we were consuming in our webpart. As we didnt assign Read permission and users's identity is used to access the resource by default,access was denied to non-admin user.

in this case, we have two solutions:
1. Grant "Read" permissions for every authenticated user.
2. Use elevated permissions(SPElevatedPermission)in code while accessing the files.

I opted second solution.

2. Then after we found that, 403 is being thrown on webservice.asmx/js file. We were using lot of ajax in webpart. this particular webpart was contacting autocompleteservice.asmx to get the suggestions for autocomplete textbox. When asp.net ajax make call to webservice through client, it creates javascript proxy on the file. You can view this java script proxy by appending /js afte webservice url.
(For instance, if your webservice is available at http://somehost/webservice.asmx, you can view it's java script proxy by typing http://somehost/webservice.asmx/js in ur browser address bar.But make sure that your webservice are marked with [ScriptService] in your code otherwise the java script proxy won't be generated.)

More Coming in next post soon....