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Re: Problems with authenticated background downloads involving a 301 redirect
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Re: Problems with authenticated background downloads involving a 301 redirect


  • Subject: Re: Problems with authenticated background downloads involving a 301 redirect
  • From: Scott Hancher <email@hidden>
  • Date: Wed, 23 Jul 2014 13:56:53 -0700

This took some time to figure out how to decipher the initial request and redirected request. I did manage to get Charles Proxy to decipher the data for me, but it didn't work until I pulled this line:

_configuration.TLSMinimumSupportedProtocol = kTLSProtocol12;

With this line in place I kept getting an SSLHandshake failed problem.

Now that I can trace the requests, I've determined that this is NOT specific to background downloads. Within the initial request, we add an 'Authorization' header to the request. When our server redirects via a 301, the subsequent redirected request does not include this 'Authorization' header. I added an innocuous foo:bar header just to see if all headers were getting stripped, but foo:bar survived the redirect. This was working for foreground downloads, because we implement the delegate method, URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler: and carry over the 'Authorization' header from the original to the redirected request. We have no such facility to do so for background downloads.

Is this a known issue? What do you suggest?

++Scott.



On Mon, Jul 21, 2014 at 2:18 AM, Quinn "The Eskimo!" <email@hidden> wrote:

On 19 Jul 2014, at 00:23, Scott Hancher <email@hidden> wrote:

> I'm downloading files from our servers using an https scheme and an OAuth 2 'Authorization' header. The server receiving the request redirects via a 301 to a different URL for the actual file to download.
>
> The download works without issue if it's performed in the foreground (NSURLSession created with an NSURLSessionConfiguration created via [NSURLSessionConfiguration ephemeralSessionConfiguration]).
>
> However, if a background download is attempted (using [NSURLSessionConfiguration backgroundSessionConfiguration:] to construct the NSURLSessionConfiguration), then the download fails via a 403 status code.

Do you have any cookies involved?  The one case I've seen similar to this involves NSURLSession background sessions not picking up cookies on the redirect <rdar://problem/16852027>.

If there are no cookies involved then I recommend you take a packet trace of the two requests (the one from the ephemeral session and the one from the background session) and see what's different, that is, what's causing the server to fail the request.

Share and Enjoy
--
Quinn "The Eskimo!"                    <http://www.apple.com/developer/>
Apple Developer Relations, Developer Technical Support, Core OS/Hardware



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  • Follow-Ups:
    • Re: Problems with authenticated background downloads involving a 301 redirect
      • From: "Quinn \"The Eskimo!\"" <email@hidden>
    • Re: Problems with authenticated background downloads involving a 301 redirect
      • From: Andreas Fink <email@hidden>
References: 
 >Problems with authenticated background downloads involving a 301 redirect (From: Scott Hancher <email@hidden>)
 >Re: Problems with authenticated background downloads involving a 301 redirect (From: "Quinn \"The Eskimo!\"" <email@hidden>)

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