add new @actions/attest package

Signed-off-by: Brian DeHamer <[email protected]>

packages/attest/src/intoto.ts

@@ -0,0 +1,32 @@
+import {Predicate, Subject} from './shared.types'
+
+const INTOTO_STATEMENT_V1_TYPE = 'https://in-toto.io/Statement/v1'
+
+/**
+ * An in-toto statement.
+ * https://github.com/in-toto/attestation/blob/main/spec/v1/statement.md
+ */
+export type InTotoStatement = {
+  _type: string
+  subject: Subject[]
+  predicateType: string
+  predicate: object
+}
+
+/**
+ * Assembles the given subject and predicate into an in-toto statement.
+ * @param subject - The subject of the statement.
+ * @param predicate - The predicate of the statement.
+ * @returns The constructed in-toto statement.
+ */
+export const buildIntotoStatement = (
+  subject: Subject,
+  predicate: Predicate
+): InTotoStatement => {
+  return {
+    _type: INTOTO_STATEMENT_V1_TYPE,
+    subject: [subject],
+    predicateType: predicate.type,
+    predicate: predicate.params
+  }
+}