AMP load-cookie updates (#3221)

dev-docs/show-prebid-ads-on-amp-pages.md

@@ -244,37 +244,45 @@ If you're using AppNexus' managed service, you would enter something like this:
   height="1"
   sandbox="allow-scripts allow-same-origin"
   frameborder="0"
-  src="https://acdn.adnxs.com/prebid/amp/user-sync/load-cookie.html?endpoint=appnexus&max_sync_count=5">
+  src="https://acdn.adnxs.com/prebid/amp/user-sync/load-cookie.html?endpoint=appnexus&max_sync_count=5&source=amp">
   <amp-img layout="fill" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==" placeholder></amp-img>
 </amp-iframe>
 ```
 
-If you are utilizing Magnite's managed service, there's an extra parameter:
+If you are utilizing Magnite's managed service, there's an extra `args` parameter:
 ```html
 <amp-iframe width="1" title="User Sync"
   height="1"
   sandbox="allow-scripts allow-same-origin"
   frameborder="0"
-  src="https://PROVIDED_BY_MAGNITE/prebid/load-cookie.html?endpoint=rubicon&max_sync_count=5&args=account:MAGNITE_ACCOUNT_ID">
+  src="https://GET_URL_FROM_MAGNITE_ACCOUNT_TEAM/prebid/load-cookie.html?endpoint=rubicon&max_sync_count=5&source=amp&args=account:MAGNITE_ACCOUNT_ID">
   <amp-img layout="fill" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==" placeholder></amp-img>
 </amp-iframe>
 ```
+
+Or you can specify a full URL to another Prebid Server location (including a QA site) by setting `endpoint` to a URL-encoded string. e.g.
+```html
+<amp-iframe width="1" title="User Sync"
+  height="1"
+  sandbox="allow-scripts allow-same-origin"
+  frameborder="0"
+  src="https://acdn.adnxs.com/prebid/amp/user-sync/load-cookie.html?endpoint=https%3A%2F%2Fprebid-server-qa.example.com%2Fcookie_sync&max_sync_count=5&source=amp">
+  <amp-img layout="fill" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==" placeholder></amp-img>
+</amp-iframe>
+```
+
 The usage of `load-cookie.html` and `load-cookie-with-consent.html` is the same. The arguments available on the query string are:
 
 {: .table .table-bordered .table-striped }
 | Param | Scope | Values | Description |
 | --- | --- | --- | --- |
-| endpoint | recommended | appnexus or rubicon | Determines which cluster of prebid servers to load from. Default, for legacy reasons, is appnexus. |
+| endpoint | recommended | 'appnexus', 'rubicon', or URL | Determines which cluster of prebid servers to load from. Default, for legacy reasons, is appnexus. |
+| source | optional | recommended | Set it to 'amp' to tell Prebid Server to exclude iframe syncs, which don't work on AMP. |
 | max_sync_count | optional | integer | How many sync pixels should be returned from Prebid Server |
 | args | optional | attr1:val1,attr2:val2 | These attribute value pairs will be passed to Prebid Server in the /cookie_sync call. The attribute and value will be quoted by the system when appropriate. |
 | gdpr | optional | 0 or 1 | Defines whether GDPR processing is in scope for this request. 0=no, 1=yes. Leave unknown if not sure. |
 | gdpr_consent | optional | String | IAB CMP-formatted consent string |
 
-{% capture endpointNote %}
-Currently, if you need to sync with a Prebid Server other than appnexus or rubicon, you'll need to fork the repo, change the endpoint, and host it somewhere. There is an [issue open to resolve](https://github.com/prebid/prebid-universal-creative/issues/122) this.
-{% endcapture %}
-{% include alerts/alert_note.html content=endpointNote %}
-
 ### AMP RTC and GDPR
 
 The two Prebid Server RTC vendor strings 'prebidappnexus' and 'prebidrubicon'
@@ -283,7 +291,25 @@ support passing GDPR consent to Prebid Server.
 The CONSENT_STRING macro will be populated if you've integrated with a CMP
 that supports amp-consent v2 -- custom CMP integration.
 
-If you're using a custom RTC callout, you'll need to add `gdpr_consent=CONSENT_STRING` to the list of parameters.
+If you're using a custom RTC callout, here are the parameters that can be passed through the RTC string:
+- tag_id
+- w=ATTR(width)
+- h=ATTR(height)
+- ow=ATTR(data-override-width)
+- oh=ATTR(data-override-height)
+- ms=ATTR(data-multi-size)
+- slot=ATTR(data-slot)
+- targeting=TGT
+- curl=CANONICAL_URL
+- timeout=TIMEOUT
+- adc=ADCID
+- purl=HREF
+- gdpr_consent=CONSENT_STRING
+- consent_type=CONSENT_METADATA(consentStringType)
+- gdpr_applies=CONSENT_METADATA(gdprApplies)
+- attl_consent=CONSENT_METADATA(additionalConsent)
+
+See the entries in the [AMP vendors callout file](https://github.com/ampproject/amphtml/blob/main/src/service/real-time-config/callout-vendors.js).
 
 ## Debugging Tips
 To review that Prebid on AMP is working properly the following aspects can be looked at: