generate v0.3 bundles in attest package

Signed-off-by: Brian DeHamer <bdehamer@github.com>

packages/attest/src/attest.ts

@@ -1,10 +1,11 @@
-import {Bundle, bundleToJSON} from '@sigstore/bundle'
+import {bundleToJSON} from '@sigstore/bundle'
 import {X509Certificate} from 'crypto'
 import {SigstoreInstance, signingEndpoints} from './endpoints'
 import {buildIntotoStatement} from './intoto'
 import {Payload, signPayload} from './sign'
 import {writeAttestation} from './store'
 
+import type {Bundle} from '@sigstore/sign'
 import type {Attestation, Predicate, Subject} from './shared.types'
 
 const INTOTO_PAYLOAD_TYPE = 'application/vnd.in-toto+json'

packages/attest/src/sign.ts

@@ -1,5 +1,5 @@
-import {Bundle} from '@sigstore/bundle'
 import {
+  Bundle,
   BundleBuilder,
   CIContextProvider,
   DSSEBundleBuilder,
@@ -103,5 +103,7 @@ const initBundleBuilder = (opts: SignOptions): BundleBuilder => {
     )
   }
 
-  return new DSSEBundleBuilder({signer, witnesses})
+  // Build the bundle with the singleCertificate option which will
+  // trigger the creation of v0.3 DSSE bundles
+  return new DSSEBundleBuilder({signer, witnesses, singleCertificate: true})
 }