delegation: add predicates to check if a delegation is a root or powerline

token/delegation/delegation.go

@@ -83,7 +83,7 @@ func New(iss did.DID, aud did.DID, cmd command.Command, pol policy.Policy, sub d
 }
 
 // Root creates a validated UCAN delegation Token from the provided parameters and options.
-// This is typically used to create and give a power to an agent.
+// This is typically used to create and give power to an agent.
 //
 // You can read it as "(issuer) allows (audience) to perform (cmd+pol) on itself".
 func Root(iss did.DID, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Option) (*Token, error) {
@@ -154,6 +154,16 @@ func (t *Token) Expiration() *time.Time {
 	return t.expiration
 }
 
+// IsRoot tells if the token is a root delegation.
+func (t *Token) IsRoot() bool {
+	return t.issuer == t.subject
+}
+
+// IsPowerline tells if the token is a powerline delegation.
+func (t *Token) IsPowerline() bool {
+	return t.subject == did.Undef
+}
+
 // IsValidNow verifies that the token can be used at the current time, based on expiration or "not before" fields.
 // This does NOT do any other kind of verifications.
 func (t *Token) IsValidNow() bool {

token/delegation/delegation_test.go

@@ -20,39 +20,16 @@ const (
 	subJectCmd = "/foo/bar"
 	subjectPol = `
 [
-	[
-		"==",
-		".status",
-		"draft"
-	],
-	[
-		"all",
-		".reviewer",
-		[
-			"like",
-			".email",
-			"*@example.com"
-		]
-	],
-	[
-		"any",
-		".tags",
-		[
-			"or",
-			[
-				[
-					"==",
-					".",
-					"news"
-				],
-				[
-					"==",
-					".",
-					"press"
-				]
-			]
-		]
-	]
+  ["==", ".status", "draft"],
+  ["all", ".reviewer",
+    ["like", ".email", "*@example.com"]
+  ],
+  ["any", ".tags",
+    ["or", [
+      ["==", ".", "news"],
+      ["==", ".", "press"]
+    ]]
+  ]
 ]
 `
 
@@ -80,6 +57,9 @@ func TestConstructors(t *testing.T) {
 		)
 		require.NoError(t, err)
 
+		require.False(t, tkn.IsRoot())
+		require.False(t, tkn.IsPowerline())
+
 		data, err := tkn.ToDagJson(didtest.PersonaAlice.PrivKey())
 		require.NoError(t, err)
 
@@ -97,6 +77,9 @@ func TestConstructors(t *testing.T) {
 		)
 		require.NoError(t, err)
 
+		require.True(t, tkn.IsRoot())
+		require.False(t, tkn.IsPowerline())
+
 		data, err := tkn.ToDagJson(didtest.PersonaAlice.PrivKey())
 		require.NoError(t, err)
 
@@ -114,6 +97,9 @@ func TestConstructors(t *testing.T) {
 		)
 		require.NoError(t, err)
 
+		require.False(t, tkn.IsRoot())
+		require.True(t, tkn.IsPowerline())
+
 		data, err := tkn.ToDagJson(didtest.PersonaAlice.PrivKey())
 		require.NoError(t, err)