Injecting native asset.id

[bretg]

Prebid.js issue prebid/Prebid.js#8317 updated the PBS adapter to inject asset.ids for native. The imp.native.asset[].id field is required by the ORTB 1.2 Native spec, but not sent by PBJS.

Currently PBS has one native-specific feature documented at https://docs.prebid.org/prebid-server/features/pbs-native.html, but is mostly a pass-through.

I propose that we add a host-level option to turn off the injection of sequential asset ids:

1. Check the host-level config (e.g. settings.native.insert-asset-ids). If it exists and is 'false', stop. Otherwise continue. (i.e. the feature is on by default)
2. For each imp in the request, check to see if imp[].native exists. If not, go to the next imp.
3. If imp[].native exists, scan the imp[].native.assets[] array to find out if any of the assets already have an ID. If any do, then no action is taken. PBS will not attempt to insert IDs for input that has a mix of blank and specified IDs.
4. If there's no entry in the imp[].native.assets[] array that contains an id, then create an id element for all of them, starting at 1 and incrementing by 1. i.e. imp[N].native.assets[0].id=1, imp[N].native.assets[1].id=2, etc.

[SyntaxNode]

This feature already exists in PBS-Go with the following slight differences:

• This feature is always enabled there is no config flag to disable it.
• The computed native ids start at 0 and auto-increment, instead of starting at 1.

[bretg]

I confirmed it's already done in PBS-Java too. Makes me wonder why @jsnellbaker needed to do this the pbsBidAdapter? Anyhow, closing this issue.

[bretg]

Updated the docs in prebid/prebid.github.io#3746