cheery pick UTC fix from main (#545)

Author: MattB-msft

src/libraries/Core/Microsoft.Agents.Core/Models/TokenResponse.cs

@@ -24,7 +24,9 @@ public TokenResponse(string channelId = default, string connectionName = default
             ChannelId = channelId;
             ConnectionName = connectionName;
             Token = token;
-            Expiration = expiration;
+
+            if (expiration != default) // do not set the expiration if the default value is passed. If the timezone is + UTC it will cause a fault when assigned as an offset.
+                Expiration = expiration;
         }
 
         /// <summary> The channelId of the TokenResponse. </summary>