buildx(build): resolveProvenance from metadata

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

src/buildx/build.ts

@@ -25,6 +25,7 @@ import {GitHub} from '../github';
 import {Util} from '../util';
 
 import {BuildMetadata} from '../types/buildx/build';
+import {ProvenancePredicate} from '../types/intoto/slsa_provenance/v0.2/provenance';
 
 export interface BuildOpts {
   buildx?: Buildx;
@@ -82,6 +83,19 @@ export class Build {
     return undefined;
   }
 
+  public resolveProvenance(metadata?: BuildMetadata): ProvenancePredicate | undefined {
+    if (!metadata) {
+      metadata = this.resolveMetadata();
+      if (!metadata) {
+        return undefined;
+      }
+    }
+    if ('buildx.build.provenance' in metadata) {
+      return metadata['buildx.build.provenance'] as ProvenancePredicate;
+    }
+    return undefined;
+  }
+
   public resolveDigest(metadata?: BuildMetadata): string | undefined {
     if (!metadata) {
       metadata = this.resolveMetadata();

src/types/buildx/build.ts

@@ -15,5 +15,6 @@
  */
 
 export type BuildMetadata = {
-  [key: string]: string;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  [key: string]: any;
 };