WIP

token/delegation/delegation.go

@@ -172,6 +172,25 @@ func (t *Token) IsValidAt(ti time.Time) bool {
 	return true
 }
 
+// Covers indicate if this token has the power to allow the given sub-delegation.
+// This function only verifies the principals alignment
+func (t *Token) Covers(subDelegation *Token) bool {
+	// The Subject of each delegation must equal the invocation's Subject (or Audience if defined). - 4f
+	if t.Subject() != sub {
+		return fmt.Errorf("%w: delegation %s, expected %s, got %s", ErrWrongSub, dlgCid, sub, dlg.Subject())
+	}
+
+	// The Issuer of each delegation must be the Audience in the next one. - 4d
+	if t.Audience() != subDelegation.Issuer() {
+		return fmt.Errorf("%w: delegation %s, expected %s, got %s", ErrBrokenChain, dlgCid, iss, dlg.Audience())
+	}
+
+	// The command of each delegation must "allow" the one before it. - 4g
+	if !dlg.Command().Covers(cmd) {
+		return fmt.Errorf("%w: delegation %s, %s doesn't cover %s", ErrCommandNotCovered, dlgCid, dlg.Command(), cmd)
+	}
+}
+
 func (t *Token) String() string {
 	var res strings.Builder
 

token/invocation/proof.go

@@ -37,9 +37,9 @@ import (
 //  4. When the proof chain is being validated (verifyProofs below):
 //     a. There must be at least one delegation in the proof chain.
 //     b. All referenced delegations must be available.
-//     c. The first proof must be issued to the Invoker (audience DID).
+//     c. The first proof must be issued to the Invoker.
-//     d. The Issuer of each delegation must be the Audience in the next one.
+//     d. The Issuer of each delegation must be the Audience in the parent delegation.
-//     e. The last token must be a root delegation.
+//     e. The chain must terminate with a root delegation.
 //     f. The Subject of each delegation must equal the invocation's Subject (or Audience if defined)
 //     g. The command of each delegation must "allow" the one before it.
 //
@@ -72,7 +72,7 @@ func (t *Token) verifyProofs(delegations []*delegation.Token) error {
 			return fmt.Errorf("%w: delegation %s, expected %s, got %s", ErrWrongSub, dlgCid, sub, dlg.Subject())
 		}
 
-		// The first proof must be issued to the Invoker (audience DID). - 4c
+		// The first proof must be issued to the Invoker. - 4c
 		// The Issuer of each delegation must be the Audience in the next one. - 4d
 		if dlg.Audience() != iss {
 			return fmt.Errorf("%w: delegation %s, expected %s, got %s", ErrBrokenChain, dlgCid, iss, dlg.Audience())