PS: I tested access from my home account and verified that the external permission problem is real.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/8a27c2e6934a8fe2c223f854d4972d0030f5b2cb

commit 8a27c2e6934a8fe2c223f854d4972d0030f5b2cb
Author: Don Garrett <dgarrett@chromium.org>
Date: Mon Aug 01 20:28:40 2016

Revert "report_stage: No longer generate HTML index."

This reverts commit 8f19fd9e85cf7e16a918e7c10bae3629d1a353fe.

The index file is used to display lists of artifacts for public users
as they don't have permission to browse buckets.

BUG= chromium:633330 
TEST=run_tests

Change-Id: I113bffc613b1c1d75e036aa1a8d6a2cb17460e8f
Reviewed-on: https://chromium-review.googlesource.com/365040
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/8a27c2e6934a8fe2c223f854d4972d0030f5b2cb/cbuildbot/stages/report_stages_unittest.py
[modify] https://crrev.com/8a27c2e6934a8fe2c223f854d4972d0030f5b2cb/cbuildbot/stages/report_stages.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/13cbbff88d23d11811580198e77d5c19cfc7ab8e

commit 13cbbff88d23d11811580198e77d5c19cfc7ab8e
Author: Don Garrett <dgarrett@google.com>
Date: Tue Aug 09 21:18:38 2016

commands: Simplify GenerateHtmlIndex signature.

Adjust GenerateHtmlIndex so we pass in the title, not the entire HTML
header and body opener in a fragile way.

BUG= chromium:633330 
TEST=Unittests

Change-Id: I20dfcfce1ac96cd7aabad385fe1d5e2b970cb7de
Reviewed-on: https://chromium-review.googlesource.com/367514
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>

[modify] https://crrev.com/13cbbff88d23d11811580198e77d5c19cfc7ab8e/scripts/upload_prebuilts.py
[modify] https://crrev.com/13cbbff88d23d11811580198e77d5c19cfc7ab8e/cbuildbot/commands.py
[modify] https://crrev.com/13cbbff88d23d11811580198e77d5c19cfc7ab8e/cbuildbot/stages/report_stages.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/f3d81f6f5e2cf48203efb4612347c031301026ef

commit f3d81f6f5e2cf48203efb4612347c031301026ef
Author: Don Garrett <dgarrett@google.com>
Date: Tue Aug 09 21:31:49 2016

report_stages: Move archive_urls linking from results_lib.

Generating links to the build artifacts properly belongs in the report
stage, not in the results_lib that (other than this) only reports on
stage pass/fail.

BUG= chromium:633330 
TEST=run_tests

Change-Id: I1a7589a1ad87cb469feccdc78224f3bfcd7a4b1f
Reviewed-on: https://chromium-review.googlesource.com/367515
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>

[modify] https://crrev.com/f3d81f6f5e2cf48203efb4612347c031301026ef/cbuildbot/results_lib_unittest.py
[modify] https://crrev.com/f3d81f6f5e2cf48203efb4612347c031301026ef/cbuildbot/results_lib.py
[modify] https://crrev.com/f3d81f6f5e2cf48203efb4612347c031301026ef/cbuildbot/stages/report_stages.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/9df16c30b34e6a226ab6824de16951174b3498c4

commit 9df16c30b34e6a226ab6824de16951174b3498c4
Author: Don Garrett <dgarrett@google.com>
Date: Tue Aug 09 22:47:51 2016

ReportStage: Adjust where artifacts are linked.

We want to generate index.html files and use them for public build
artifacts, so that public builds can be viewed from an unauthenticated
account.

However, we want to link directly to pantheon for private builds so that
developers can more easily navigate to related artifacts.

Rename _UploadArchiveIndex -> _LinkArtifacts, and move link generation
directly into it so that it can adjust the links as needed.

BUG= chromium:633330 ,  chromium:638254 
TEST=run_tests

Change-Id: If04d2c041af4a0888098952bccb3e1b910c1d83a
Reviewed-on: https://chromium-review.googlesource.com/367516
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>

[modify] https://crrev.com/9df16c30b34e6a226ab6824de16951174b3498c4/cbuildbot/stages/report_stages_unittest.py
[modify] https://crrev.com/9df16c30b34e6a226ab6824de16951174b3498c4/cbuildbot/stages/report_stages.py

Issue 650400 has been merged into this issue.

 Issue 669148  has been merged into this issue.

 Issue 707874  has been merged into this issue.

This bit me today trying to download a VM image from:
https://build.chromium.org/p/chromiumos.chromium/builders/amd64-generic-tot-chromium-pfq-informational/builds/12190

Not actively working on this. Back to triage queue.

Got to this issue after trying to download qemu image. Any info when this will be fixed? 

Ran into this again.

You can use links like these instead:
https://pantheon.corp.google.com/storage/browser/chromeos-image-archive/amd64-generic-full/R65-10232.0.0-b20665/

https://chromium-review.googlesource.com/846537

Apparently link 
https://pantheon.corp.google.com/storage/browser/chromeos-image-archive/amd64-generic-full/R65-10232.0.0-b20665/

opens SSO page used for Google employees authentication. 

Any non Google employee will not be able to download images. 
Initial problem still exists, we can't download images from artifacts. 

Right, for non-Googlers, you can prepend:
https://storage.cloud.google.com/chromeos-image-archive/amd64-generic-full/R65-10232.0.0-b20665/

Clicking on the above link without a specific target doesn't work. So to see the UPLOADED file, you'd go to:
https://storage.cloud.google.com/chromeos-image-archive/amd64-generic-full/R65-10232.0.0-b20665/UPLOADED

The CL in comment #16 fixes this, so hopefully we can land it soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/03d924ada94bc2f599e81f4b0422f2b015e0aa1a

commit 03d924ada94bc2f599e81f4b0422f2b015e0aa1a
Author: Achuith Bhandarkar <achuith@chromium.org>
Date: Fri Jan 05 11:14:38 2018

[cbuildbot]: Fix artifacts/prebuilts index.html for external builds.

BUG= chromium:633330 
TEST=None

Change-Id: If7f85cfa0ec5c5a96b9c943d797611033d0a1892
Reviewed-on: https://chromium-review.googlesource.com/846537
Commit-Ready: Achuith Bhandarkar <achuith@chromium.org>
Tested-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/03d924ada94bc2f599e81f4b0422f2b015e0aa1a/scripts/upload_prebuilts.py
[modify] https://crrev.com/03d924ada94bc2f599e81f4b0422f2b015e0aa1a/cbuildbot/stages/report_stages.py

Looks like the last CL worked.

Here's a recent build of amd64-generic-full:
https://uberchromegw.corp.google.com/i/chromiumos/builders/amd64-generic-full/builds/20829

Artifacts link:
https://storage.cloud.google.com/chromeos-image-archive/amd64-generic-full/R65-10281.0.0-b20829/index.html

And clicking on the links in this page works. 

This is the link for prebuilts:
https://storage.googleapis.com/chromeos-prebuilt/board/amd64-generic/full-2018.01.05.062218/packages/index.html

We don't seem to surface this link the build page, I got it from the log file of the UploadPrebuilts stage:
https://logs.chromium.org/v/?s=chromiumos%2Fbb%2Fchromiumos%2Famd64-generic-full%2F20829%2F%2B%2Frecipes%2Fsteps%2FUploadPrebuilts%2F0%2Fstdout

Anyway, the links work here as well.

Closing as fixed.

the artifacts index is linked as part of the Report stage at the end

Yup, but there's no equivalent chromeos-prebuilt index.html link anywhere.

right ... that one we don't emit a direct link for