whitelist Authorization header via SharedVarnishConstants

[davidsbailey]

follow-on to #26383 to allow Authorization header through Varnish and CloudFront. HttpCache cannot depend on SharedConstants because that file is not available in chef, so we have to jump through some extra hoops.

[davidsbailey]

@sureshc , can you please review? CC @wjordan . Main points of interest are (1) HttpCache config and (2) the arrangement of the shared constants between lib/cdo and HttpCache.

I've verified on an adhoc that this is working end-to-end now to access spotify URLs via the startWebRequest block in App Lab. You can see it working here: https://adhoc-spotify-whitelist-studio.cdn-code.org/projects/applab/TP3c4-GKEI4pvQ5HayE-1w/view

although the access token expires after just a few minutes so if you get a 401 I may just need to update the program with a new access token

[wjordan]

@davidsbailey glad you got this working. I don't know if it was necessary to create a new module to reference this constant 'without pulling in anything else in HttpCache', as we already have several shared constants in HttpCache (referenced through ScriptConfig) similarly used by Dashboard.

In any case, maintaining two different places for storing the same type of constant is now less than ideal. Either we should move the existing script constants out of HttpCache into SharedVarnishConstants or move the newly-added constant from SharedVarnishConstants into HttpCache, removing the new module.

[davidsbailey]

Apologies @wjordan for merging this before you had a chance to respond. That's fine, I can merge SharedVarnishConstants into HttpCache. Please see follow-on PR #26553 .