macaroons: specify root key ID in bakery

macaroons/context.go

@@ -0,0 +1,44 @@
+package macaroons
+
+import (
+	"context"
+	"fmt"
+)
+
+var (
+	// RootKeyIDContextKey is the key to get rootKeyID from context.
+	RootKeyIDContextKey = contextKey{"rootkeyid"}
+
+	// ErrContextRootKeyID is used when the supplied context doesn't have
+	// a root key ID.
+	ErrContextRootKeyID = fmt.Errorf("failed to read root key ID " +
+		"from context")
+)
+
+// contextKey is the type we use to identify values in the context.
+type contextKey struct {
+	Name string
+}
+
+// ContextWithRootKeyID passes the root key ID value to context.
+func ContextWithRootKeyID(ctx context.Context,
+	value interface{}) context.Context {
+
+	return context.WithValue(ctx, RootKeyIDContextKey, value)
+}
+
+// RootKeyIDFromContext retrieves the root key ID from context using the key
+// RootKeyIDContextKey.
+func RootKeyIDFromContext(ctx context.Context) ([]byte, error) {
+	id, ok := ctx.Value(RootKeyIDContextKey).([]byte)
+	if !ok {
+		return nil, ErrContextRootKeyID
+	}
+
+	// Check that the id is not empty.
+	if len(id) == 0 {
+		return nil, ErrMissingRootKeyID
+	}
+
+	return id, nil
+}