Add support for Fulcio and Rekor, and --sign-by-sigstore=param-file

(skopeo copy) and (skopeo sync) now support --sign-by-sigstore=param-file,
using the containers-sigstore-signing-params.yaml(5) file format.

That notably adds support for Fulcio and Rekor signing.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/google.golang.org/appengine/internal/identity_classic.go

@@ -0,0 +1,61 @@
+// Copyright 2015 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+// +build appengine
+
+package internal
+
+import (
+	"appengine"
+
+	netcontext "golang.org/x/net/context"
+)
+
+func init() {
+	appengineStandard = true
+}
+
+func DefaultVersionHostname(ctx netcontext.Context) string {
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	return appengine.DefaultVersionHostname(c)
+}
+
+func Datacenter(_ netcontext.Context) string { return appengine.Datacenter() }
+func ServerSoftware() string                 { return appengine.ServerSoftware() }
+func InstanceID() string                     { return appengine.InstanceID() }
+func IsDevAppServer() bool                   { return appengine.IsDevAppServer() }
+
+func RequestID(ctx netcontext.Context) string {
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	return appengine.RequestID(c)
+}
+
+func ModuleName(ctx netcontext.Context) string {
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	return appengine.ModuleName(c)
+}
+func VersionID(ctx netcontext.Context) string {
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	return appengine.VersionID(c)
+}
+
+func fullyQualifiedAppID(ctx netcontext.Context) string {
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	return c.FullyQualifiedAppID()
+}