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/github.com/go-openapi/validate/formats.go

@@ -0,0 +1,69 @@
+// Copyright 2015 go-swagger maintainers
+//
+// 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.
+
+package validate
+
+import (
+	"reflect"
+
+	"github.com/go-openapi/spec"
+	"github.com/go-openapi/strfmt"
+)
+
+type formatValidator struct {
+	Format       string
+	Path         string
+	In           string
+	KnownFormats strfmt.Registry
+}
+
+func (f *formatValidator) SetPath(path string) {
+	f.Path = path
+}
+
+func (f *formatValidator) Applies(source interface{}, kind reflect.Kind) bool {
+	doit := func() bool {
+		if source == nil {
+			return false
+		}
+		switch source := source.(type) {
+		case *spec.Items:
+			return kind == reflect.String && f.KnownFormats.ContainsName(source.Format)
+		case *spec.Parameter:
+			return kind == reflect.String && f.KnownFormats.ContainsName(source.Format)
+		case *spec.Schema:
+			return kind == reflect.String && f.KnownFormats.ContainsName(source.Format)
+		case *spec.Header:
+			return kind == reflect.String && f.KnownFormats.ContainsName(source.Format)
+		}
+		return false
+	}
+	r := doit()
+	debugLog("format validator for %q applies %t for %T (kind: %v)\n", f.Path, r, source, kind)
+	return r
+}
+
+func (f *formatValidator) Validate(val interface{}) *Result {
+	result := new(Result)
+	debugLog("validating \"%v\" against format: %s", val, f.Format)
+
+	if err := FormatOf(f.Path, f.In, f.Format, val.(string), f.KnownFormats); err != nil {
+		result.AddErrors(err)
+	}
+
+	if result.HasErrors() {
+		return result
+	}
+	return nil
+}