internal/relui/sign: add signing server

This change adds the signing server used to request artifact signing.
An interface has been added to the sign package in order to create
different implementations of the signing service if needed. With the
GRPC signing service, the client creates a bidirectional connection
with the server. The server then sends well specified signing requests
to the client.

Updates golang/go#54303
Updates golang/go#53632

Change-Id: I062f7db716edba810b6c1dab122b2a10c1c18923
Reviewed-on: https://go-review.googlesource.com/c/build/+/422598
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Jenny Rakoczy <[email protected]>
Run-TryBot: Carlos Amedee <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: cagedmantis

internal/relui/protos/relui.pb.go

@@ -44,10 +44,15 @@ message SignArtifactRequest {
 message SigningRequest {
   // unique identifier for the signing job.
   string id = 1;
+  // unique identifier for the request. This would normally reside within
+  // the metadata. This is primarily used to route requests between
+  // caller/responder. The server and client must use the same id for each
+  // corresponging request.
+  string message_id = 2;
   // Request type for the signing client.
   oneof request_oneof {
-    SignArtifactStatusRequest status = 2;
-    SignArtifactRequest sign = 3;
+    SignArtifactStatusRequest status = 3;
+    SignArtifactRequest sign = 4;
   }
 }
 
@@ -76,11 +81,16 @@ message StatusCompleted {
 message SigningStatus {
   // unique identifier for the signing job.
   string id = 1;
+  // unique identifier for the request. This would normally reside within
+  // the metadata. This is primarily used to route requests between
+  // caller/responder. The server and client must use the same id for each
+  // corresponging request.
+  string message_id = 2;
   // The status type of the signing request.
   oneof status_oneof {
-    StatusNotFound not_found = 2;
-    StatusRunning running = 3;
-    StatusFailed failed = 4;
-    StatusCompleted completed = 5;
+    StatusNotFound not_found = 3;
+    StatusRunning running = 4;
+    StatusFailed failed = 5;
+    StatusCompleted completed = 6;
   }
 }

internal/relui/protos/relui.proto

@@ -0,0 +1,7 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package sign provides implementations for servers which can
+// sign Go release artifacts.
+package sign