switch from updateOne to findOneAndUpdate to return new document

app/services/oauth2.js

@@ -178,7 +178,7 @@ class OAuth2Service extends SiteService {
      * calling host.
      */
 
-    const client = await OAuth2Client.updateOne(
+    const client = await OAuth2Client.findOneAndUpdate(
       {
         'site.domain': clientDefinition.domain,
         'site.domainKey': clientDefinition.domainKey,
@@ -199,7 +199,10 @@ class OAuth2Service extends SiteService {
           redirectUri: clientDefinition.coreAuth.redirectUri,
         },
       },
-      { upsert: true, returnDocument: true },
+      {
+        upsert: true, // create if it doesn't exist
+        "new": true,  // return the modified version
+      },
     );
 
     this.log.info('new OAuth2 client updated', {