Bid Adapters should be able to specify custom targeting

[bretg]

Related tangentially to issue #2030

We discussed in committee that client-side adapters have the ability to supply custom targeting to the ad server. Server-side adapters should be able to do this as well.

We should define a syntax for where adapters can place the custom targeting. If it exists, PBS-core should copy it to the output seatbid.bid.ext.prebid.targeting (or for AMP, that special output format).

In order for publishers to be able to control this targeting, a new targeting control is proposed:

ext.prebid: {
  targeting: {
    ...
    includecustomkeys: ["bidderA"]     // default to "*". Set to empty string ("") to indicate none.
  }
}

Requirements:

1. if a bidder places custom targeting in their response object, PBS-core must check the includecustomkeys parameter. If it doesn't exist, default to "*".
2. If includecustomkeys is "", then ignore custom bidder targeting
3. If includecustomkeys is "*", accept all custom bidder targeting by placing it on seatbid.bid.ext.prebid.targeting
4. If includecustomkeys is an array of strings, check that the bidder's code is present on the array. If it is, then place it in seatbid.bid.ext.prebid.targeting
5. This behavior should happen after the processing of includewinners, includebidderkeys, and includeformat.
6. If a key that would be added is already in the destination, log a debug warning: "Not adding duplicate targeting key BLAH for bidder FOO."
7. if a publisher supplies an invalid bidder, it is ignored.
8. bidder name comparison should be case insensitive

[SyntaxNode]

Hey @bretg, is this actually a duplicate of #289?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[bretg]

Yup, duplicate. This one's better-defined so closed the other.