fix(rpc): pass auth credentials into duplex streams

bin/template/duplex-stream-method.tmpl

@@ -1,4 +1,6 @@
 --<%= getCommentPrefixing(`rpc ${name}(`) %>
   public <%= _.lowerFirst(name) %>(): Promise<IDuplexStream<<%= requestTsType %>, <%= responseTsType %>>> {
-    return this.client.getConnection('<%= service %>').then(cnx => (<any> cnx.client).<%= _.lowerFirst(name) %>());
+    return this.client
+      .getConnection('<%= service %>')
+      .then(({ client, metadata }) => (<any> client).<%= _.lowerFirst(name) %>(metadata));
   }

bin/template/rpc-prefix.tmpl

@@ -5,7 +5,7 @@ import * as grpc from 'grpc';
 
 export interface ICallable {
   exec(service: keyof typeof Services, method: string, params: object): Promise<any>;
-  getConnection(service: keyof typeof Services): Promise<{ client: grpc.Client }>;
+  getConnection(service: keyof typeof Services): Promise<{ client: grpc.Client, metadata: grpc.Metadata }>;
 }
 
 export interface IResponseStream<T> {