Add issuance chain cache interface

trillian/ctfe/cache/cache.go

@@ -0,0 +1,27 @@
+// Copyright 2024 Google LLC
+//
+// 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 cache defines the IssuanceChainCache type, which allows different cache implementation with Get and Set operations.
+package cache
+
+import "context"
+
+// IssuanceChainCache is an interface which allows CTFE binaries to use different cache implementations for issuance chains.
+type IssuanceChainCache interface {
+	// Get returns the issuance chain associated with the provided hash.
+	Get(ctx context.Context, key []byte) ([]byte, error)
+
+	// Set inserts the key-value pair of issuance chain.
+	Set(ctx context.Context, key []byte, chain []byte) error
+}