Problem

Publishers are unable to test and run experiments natively in Prebid and must rely on partners to help set up tests & control groups when they want to test various setConfig() objects.

example

A publisher may wish to test CPM change for 2 different setConfig()s

1

 pbjs.setConfig({
     userSync: {
         userIds: [{
             name: "sharedId",
             storage: {
                 type: "cookie",
                 name: "_sharedid",         
                 expires: 365         
             }
         }]
     }
 });

2

 pbjs.setConfig({
     userSync: {
         userIds: [{
             name: "OtherID",
             storage: {
                 type: "cookie",
                 name: "_OtherID",       
                 expires: 365             
             }
         }]
     }
 });

UseCase

1. As a publisher I want to test how my inventory monetizes when I include a userid module subadapter like sharedid, I want to be able to compare the presence of sharedid against no user id at all.
2. 1. As a publisher I want to test how my inventory monetizes when I include a userid module subadapter like sharedid, I want to be able to compare the presence of sharedid against a different user id such as "OtherID"

Requirements

1. setConfig() should support a sample rate int for the test cohort. Where n percent of the time the setConfig() loads one way, and n of the time it loads a different way.
2. Prebid must signal back to the publisher what imps were part of the test and which were part of the control.
   ex.

• configureable response endpoint where Impression id and cohort label (test or control) are logged.

curl --location 'http://pub.com/prebid/experiement?
--header 'Content-Type: application/json' \
--data '{
  "entries": [
    {
      "impression": 12345,
      "cohort": "test" //control
    }
  ]
}'