Implement Broker Redirects for Session and Messages

src/Sdk/DTWebApi/WebApi/BrokerMigrationMessage.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Runtime.Serialization;
+
+namespace GitHub.DistributedTask.WebApi
+{
+    /// <summary>
+    /// Represents a session for performing message exchanges from an agent.
+    /// </summary>
+    [DataContract]
+    public class BrokerMigrationMessage
+    {
+
+        public static readonly string MessageType = "BrokerMigration";
+
+        public BrokerMigrationMessage()
+        {
+        }
+
+        public BrokerMigrationMessage(
+            Uri brokerUrl)
+        {
+            this.BrokerBaseUrl = brokerUrl;
+        }
+
+        /// <summary>
+        /// Gets the unique identifier for this session.
+        /// </summary>
+        [DataMember]
+        public Uri BrokerBaseUrl
+        {
+            get;
+            internal set;
+        }
+    }
+}

src/Sdk/DTWebApi/WebApi/TaskAgentSession.cs

@@ -75,5 +75,12 @@ namespace GitHub.DistributedTask.WebApi
             get;
             set;
         }
+
+        [DataMember(EmitDefaultValue = false, IsRequired = false)]
+        public BrokerMigrationMessage BrokerMigrationMessage
+        {
+            get;
+            set;
+        }
     }
 }