Various fixes (#63)

* Fix digest resolution and attestation style

* Add a bunch more tests

* Rename fields for consistency

* Remove copy-pasta

* Value -> pointer

test/testdata/local-policy/doi/policy.rego

@@ -0,0 +1,49 @@
+package attest
+
+import rego.v1
+
+keys := [{
+	"id": "a0c296026645799b2a297913878e81b0aefff2a0c301e97232f717e14402f3e4",
+	"key": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEgH23D1i2+ZIOtVjmfB7iFvX8AhVN\n9CPJ4ie9axw+WRHozGnRy99U2dRge3zueBBg2MweF0zrToXGig2v3YOrdw==\n-----END PUBLIC KEY-----",
+	"from": "2023-12-15T14:00:00Z",
+	"to": null,
+	"status": "active",
+	"signing-format": "dssev1",
+}]
+
+provs(pred) := p if {
+	res := attest.fetch(pred)
+	not res.error
+	p := res.value
+}
+
+atts := union({
+	provs("https://slsa.dev/provenance/v0.2"),
+	provs("https://spdx.dev/Document"),
+})
+
+opts := {"keys": keys}
+
+statements contains s if {
+	some att in atts
+	res := attest.verify(att, opts)
+	not res.error
+	s := res.value
+}
+
+subjects contains subject if {
+	some statement in statements
+	some subject in statement.subject
+}
+
+result := {
+	"success": count(atts) > 0,
+	"violations": set(),
+	"attestations": statements,
+	"summary": {
+		"subjects": subjects,
+		"slsa_level": "SLSA_BUILD_LEVEL_3",
+		"verifier": "docker-official-images",
+		"policy_uri": "https://docker.com/official/policy/v0.1",
+	},
+}

test/testdata/local-policy/mapping.yaml

@@ -0,0 +1,29 @@
+# map repos to policies
+version: v1
+kind: policy-mapping
+policies:
+  - origin:
+      domain: docker.io
+      prefix: library/
+    id: test-images
+    description: Local test images
+    files:
+      - path: "doi/policy.rego"
+
+mirrors:
+  - policy-id: test-images
+    mirror:
+      domains: ["*"]
+      prefix: "repo"
+  - policy-id: test-images
+    mirror:
+      domains: ["*"]
+      prefix: "library/"
+  - policy-id: test-images
+    mirror:
+      domains: ["*"]
+      prefix: "test-image"
+  - policy-id: test-images
+    mirror:
+      domains: ["*"]
+      prefix: "image-signer-verifier-test"