bug#21350: 25.0.50; Do not automatically include authorization header in HTTP redirects

[Thomas Fitzsimmons]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Here's the updated patch that I tested.  Does it look OK stylistically?
>
> Yes, but you need to change the beginning of the file so cl-lib is not
> only require when compiling but also at run-time (since cl-remove is
> not a macro but a function).

OK, I pushed the patch.  Thanks for reviewing.

I had hoped to publish a Docker image that would allow testing the
various authorization schemes across redirects, but configuring a server
to authenticate with NTLM using Free Software proved too difficult.  I
did test against a proprietary NTLM implementation, and against the two
built-in auth schemes as well.  The results were:

   |          Authenticated Redirect          |
   |-------------+---------------+------------|
   | Auth Scheme | Without Patch | With Patch |
   |-------------+---------------+------------|
   | Basic       | Works         | Works      |
   | Digest      | Fails         | Fails      |
   | NTLM        | Fails         | Works      |

I'm not sure what's wrong with the digest scheme (Firefox works), but
this patch doesn't make digest redirects worse.

Thomas