pub-api update for server-side aliases (prebid#1933)

Author: bretg

dev-docs/publisher-api-reference.md

@@ -1248,6 +1248,10 @@ If you define an alias and are using `pbjs.sendAllBids`, you must also set up ad
 + `hb_size_newalias`
 + `hb_deal_newalias`
 
+{: .alert.alert-info :}
+Creating an alias for a Prebid Server adapter is done differently. See 'extPrebid'
+config in the [`s2sConfig`](#setConfig-Server-to-Server) object.
+
 <hr class="full-rule" />
 
 <a name="module_pbjs.setConfig"></a>
@@ -1650,7 +1654,7 @@ Example config for [server-to-server]({{site.baseurl}}/dev-docs/get-started-with
 pbjs.setConfig({
     s2sConfig: {
         accountId: '1',
-        bidders: ['appnexus', 'pubmatic'],
+        bidders: ['appnexus', 'openx', 'tripleliftVideo'],
         defaultVendor: 'appnexus',
         timeout: 1000,
         adapterOptions: {
@@ -1661,9 +1665,13 @@ pbjs.setConfig({
             'openx': function(type, url, bidder) {
             const publisherId = '00000123231231'
             url += `&ri=${publisherId}`;
-
             return url
             }
+        },
+	extPrebid: {
+	    aliases: {
+                tripleliftVideo: tripleLift
+            }
         }
     }
 })
@@ -1684,7 +1692,7 @@ Additional information of `s2sConfig` properties:
 | `syncEndpoint` | Required | URL | Defines the cookie_sync endpoint for the Prebid Server cluster |
 | `userSyncLimit` | Optional | Integer | Max number of userSync URLs that can be executed by Prebid Server cookie_sync per request.  If not defined, PBS will execute all userSync URLs included in the request. |
 | `adapterOptions` | Optional | Object | Arguments will be added to resulting OpenRTB payload to Prebid Server in every impression object at request.imp[].ext.BIDDER. See the example above. |
-| `extPrebid` | Optional | Object | Arguments will be added to resulting OpenRTB payload to Prebid Server in request.ext.prebid. See video-related example below. |
+| `extPrebid` | Optional | Object | Arguments will be added to resulting OpenRTB payload to Prebid Server in request.ext.prebid. See the examples below. |
 | `syncUrlModifier` | Optional | Object | Function to modify a bidder's sync url before the actual call to the sync endpoint. Bidder must be enabled for s2sConfig. |
 
 **Notes on s2sConfig properties**
@@ -1725,7 +1733,17 @@ pbjs.setConfig({
 
 Additional options for `s2sConfig` may be enabled by including the [Server-to-Server testing module]({{site.baseurl}}/dev-docs/modules/s2sTesting.html).
 
-**ExtPrebid Convention**
+**Server-Side Aliases**
+
+You may want to run a particular bidder on the client for banner, but that same bidder on the 
+server for video. You would do this by setting a **server-side** alias. The
+[example](#setConfig-Server-to-Server) at the start of this section provides an example. Here's how it works:
+
+1. Video ad units are coded with the dynamic alias. e.g. tripleliftVideo
+1. The s2sConfig.bidders array contains 'tripleliftVideo' telling Prebid.js to direct bids for that code to the server
+1. Finally, the extPrebid.aliases line tells Prebid Server to route the 'tripleliftVideo' biddercode to the 'triplelift' server-side adapter.
+
+**Passing the Referrer to Server Side Adapters**
 
 * Setting `extPrebid.origreferrer` will be recognized by some server-side adapters as the referring URL for the current page.