feat(keyless): implement signing service

Signed-off-by: Jose I. Paris <[email protected]>

app/controlplane/api/controlplane/v1/signing.proto

@@ -0,0 +1,40 @@
+//
+// Copyright 2024 The Chainloop Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+syntax = "proto3";
+
+package controlplane.v1;
+
+option go_package = "github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1;v1";
+
+service SigningService {
+  rpc SigningCert (SigningCertRequest) returns (SigningCertResponse);
+}
+
+message SigningCertRequest {
+  bytes certificate_signing_request = 1;
+}
+
+message SigningCertResponse {
+  CertificateChain chain = 1;
+}
+
+message CertificateChain {
+  /*
+   * The PEM-encoded certificate chain, ordered from leaf to intermediate to root as applicable.
+   */
+  repeated string certificates = 1;
+}