Merge pull request #93 from ucan-wg/proof-rephrase

invocation: rephrase slightly the proof rules to be less confusing down the line

did/did.go

@@ -102,6 +102,9 @@ func (d DID) PubKey() (crypto.PubKey, error) {
 
 // String formats the decentralized identity document (DID) as a string.
 func (d DID) String() string {
+	if d == Undef {
+		return "(undefined)"
+	}
 	key, _ := mbase.Encode(mbase.Base58BTC, []byte(d.bytes))
 	return "did:key:" + key
 }

pkg/container/serial_test.go

@@ -160,13 +160,12 @@ func randToken() (*delegation.Token, cid.Cid, []byte) {
 
 	opts := []delegation.Option{
 		delegation.WithExpiration(time.Now().Add(time.Hour)),
-		delegation.WithSubject(iss),
 	}
 	for i := 0; i < 3; i++ {
 		opts = append(opts, delegation.WithMeta(randomString(8), randomString(10)))
 	}
 
-	t, err := delegation.New(iss, aud, cmd, pol, opts...)
+	t, err := delegation.Root(iss, aud, cmd, pol, opts...)
 	if err != nil {
 		panic(err)
 	}

token/delegation/delegation.go

@@ -10,8 +10,10 @@ package delegation
 // TODO: change the "delegation" link above when the specification is merged
 
 import (
+	"encoding/base64"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/ucan-wg/go-ucan/did"
@@ -44,16 +46,15 @@ type Token struct {
 	expiration *time.Time
 }
 
-// New creates a validated Token from the provided parameters and options.
+// New creates a validated delegation Token from the provided parameters and options.
+// This is typically used to delegate a given power to another agent.
 //
-// When creating a delegated token, the Issuer's (iss) DID is assembled
+// You can read it as "(issuer) allows (audience) to perform (cmd+pol) on (subject)".
-// using the public key associated with the private key sent as the first
+func New(iss did.DID, aud did.DID, cmd command.Command, pol policy.Policy, sub did.DID, opts ...Option) (*Token, error) {
-// parameter.
-func New(iss, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Option) (*Token, error) {
 	tkn := &Token{
 		issuer:   iss,
 		audience: aud,
-		subject:  did.Undef,
+		subject:  sub,
 		command:  cmd,
 		policy:   pol,
 		meta:     meta.NewMeta(),
@@ -81,16 +82,27 @@ func New(iss, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Optio
 	return tkn, nil
 }
 
-// Root creates a validated UCAN delegation Token from the provided
+// Root creates a validated UCAN delegation Token from the provided parameters and options.
-// parameters and options.
+// This is typically used to create and give a power to an agent.
 //
-// When creating a root token, both the Issuer's (iss) and Subject's
+// You can read it as "(issuer) allows (audience) to perform (cmd+pol) on itself".
-// (sub) DIDs are assembled from the public key associated with the
+func Root(iss did.DID, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Option) (*Token, error) {
-// private key passed as the first argument.
+	return New(iss, aud, cmd, pol, iss, opts...)
-func Root(iss, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Option) (*Token, error) {
+}
-	opts = append(opts, WithSubject(iss))
 
-	return New(iss, aud, cmd, pol, opts...)
+// Powerline creates a validated UCAN delegation Token from the provided parameters and options.
+//
+// Powerline is a pattern for automatically delegating all future delegations to another agent regardless of Subject.
+// This is a very powerful pattern, use it only if you understand it.
+// Powerline delegations MUST NOT be used as the root delegation to a resource
+//
+// A very common use case for Powerline is providing a stable DID across multiple agents (e.g. representing a user with
+// multiple devices). This enables the automatic sharing of authority across their devices without needing to share keys
+// or set up a threshold scheme. It is also flexible, since a Powerline delegation MAY be revoked.
+//
+// You can read it as "(issuer) allows (audience) to perform (cmd+pol) on anything".
+func Powerline(iss did.DID, aud did.DID, cmd command.Command, pol policy.Policy, opts ...Option) (*Token, error) {
+	return New(iss, aud, cmd, pol, did.Undef, opts...)
 }
 
 // Issuer returns the did.DID representing the Token's issuer.
@@ -160,6 +172,32 @@ func (t *Token) IsValidAt(ti time.Time) bool {
 	return true
 }
 
+func (t *Token) String() string {
+	var res strings.Builder
+
+	var kind string
+	switch {
+	case t.issuer == t.subject:
+		kind = " (root delegation)"
+	case t.subject == did.Undef:
+		kind = " (powerline delegation)"
+	default:
+		kind = " (normal delegation)"
+	}
+
+	res.WriteString(fmt.Sprintf("Issuer: %s\n", t.Issuer()))
+	res.WriteString(fmt.Sprintf("Audience: %s\n", t.Audience()))
+	res.WriteString(fmt.Sprintf("Subject: %s%s\n", t.Subject(), kind))
+	res.WriteString(fmt.Sprintf("Command: %s\n", t.Command()))
+	res.WriteString(fmt.Sprintf("Policy: %s\n", t.Policy()))
+	res.WriteString(fmt.Sprintf("Nonce: %s\n", base64.StdEncoding.EncodeToString(t.Nonce())))
+	res.WriteString(fmt.Sprintf("Meta: %s\n", t.Meta()))
+	res.WriteString(fmt.Sprintf("NotBefore: %v\n", t.NotBefore()))
+	res.WriteString(fmt.Sprintf("Expiration: %v", t.Expiration()))
+
+	return res.String()
+}
+
 func (t *Token) validate() error {
 	var errs error
 

token/delegation/delegation_test.go

@@ -56,9 +56,6 @@ const (
 ]
 `
 
-	newCID  = "zdpuAwa4qv3ncMDPeDoqVxjZy3JoyWsbqUzm94rdA1AvRFkkw"
-	rootCID = "zdpuAkgGmUp5JrXvehGuuw9JA8DLQKDaxtK3R8brDQQVC2i5X"
-
 	aesKey = "xQklMmNTnVrmaPBq/0pwV5fEwuv/iClF5HWak9MsgI8="
 )
 
@@ -75,9 +72,8 @@ func TestConstructors(t *testing.T) {
 	require.NoError(t, err)
 
 	t.Run("New", func(t *testing.T) {
-		tkn, err := delegation.New(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol,
+		tkn, err := delegation.New(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol, didtest.PersonaCarol.DID(),
 			delegation.WithNonce([]byte(nonce)),
-			delegation.WithSubject(didtest.PersonaAlice.DID()),
 			delegation.WithExpiration(exp),
 			delegation.WithMeta("foo", "fooo"),
 			delegation.WithMeta("bar", "barr"),
@@ -106,6 +102,23 @@ func TestConstructors(t *testing.T) {
 
 		golden.Assert(t, string(data), "root.dagjson")
 	})
+
+	t.Run("Powerline", func(t *testing.T) {
+		t.Parallel()
+
+		tkn, err := delegation.Powerline(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol,
+			delegation.WithNonce([]byte(nonce)),
+			delegation.WithExpiration(exp),
+			delegation.WithMeta("foo", "fooo"),
+			delegation.WithMeta("bar", "barr"),
+		)
+		require.NoError(t, err)
+
+		data, err := tkn.ToDagJson(didtest.PersonaAlice.PrivKey())
+		require.NoError(t, err)
+
+		golden.Assert(t, string(data), "powerline.dagjson")
+	})
 }
 
 func TestEncryptedMeta(t *testing.T) {
@@ -153,7 +166,7 @@ func TestEncryptedMeta(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 
-			tkn, err := delegation.New(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol,
+			tkn, err := delegation.Root(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol,
 				delegation.WithEncryptedMetaString(tt.key, tt.value, encryptionKey),
 			)
 			require.NoError(t, err)
@@ -191,7 +204,7 @@ func TestEncryptedMeta(t *testing.T) {
 		}
 
 		// Create token with multiple encrypted values
-		tkn, err := delegation.New(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol, opts...)
+		tkn, err := delegation.Root(didtest.PersonaAlice.DID(), didtest.PersonaBob.DID(), cmd, pol, opts...)
 		require.NoError(t, err)
 
 		data, err := tkn.ToDagCbor(didtest.PersonaAlice.PrivKey())

token/delegation/delegationtest/generator/generator.go

@@ -30,10 +30,11 @@ const (
 var constantNonce = []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b}
 
 type newDelegationParams struct {
-	privKey crypto.PrivKey
+	privKey crypto.PrivKey // iss
 	aud     did.DID
 	cmd     command.Command
 	pol     policy.Policy
+	sub     did.DID
 	opts    []delegation.Option
 }
 
@@ -89,8 +90,8 @@ func (g *generator) chainPersonas(personas []didtest.Persona, acc acc, vari vari
 		aud:     personas[1].DID(),
 		cmd:     delegationtest.NominalCommand,
 		pol:     policytest.EmptyPolicy,
+		sub:     didtest.PersonaAlice.DID(),
 		opts: []delegation.Option{
-			delegation.WithSubject(didtest.PersonaAlice.DID()),
 			delegation.WithNonce(constantNonce),
 		},
 	}
@@ -117,7 +118,7 @@ func (g *generator) chainPersonas(personas []didtest.Persona, acc acc, vari vari
 				p.cmd = delegationtest.AttenuatedCommand
 			}},
 			{name: "InvalidSubject", variant: func(p *newDelegationParams) {
-				p.opts = append(p.opts, delegation.WithSubject(didtest.PersonaBob.DID()))
+				p.sub = didtest.PersonaBob.DID()
 			}},
 			{name: "InvalidExpired", variant: func(p *newDelegationParams) {
 				// Note: this makes the generator not deterministic
@@ -161,7 +162,7 @@ func (g *generator) createDelegation(params newDelegationParams, name string, va
 		return cid.Undef, err
 	}
 
-	tkn, err := delegation.New(issDID, params.aud, params.cmd, params.pol, params.opts...)
+	tkn, err := delegation.New(issDID, params.aud, params.cmd, params.pol, params.sub, params.opts...)
 	if err != nil {
 		return cid.Undef, err
 	}

token/delegation/delegationtest/token_gen.go

@@ -107,21 +107,21 @@ var (
 )
 
 var (
-	TokenCarolDan_InvalidExpiredCID    = cid.MustParse("bafyreigvdcarp6426e5aenal3q3c4uyhncwfbmt3fsmb4qzspkpjy57gti")
+	TokenCarolDan_InvalidExpiredCID    = cid.MustParse("bafyreifyzm5jkx2sfu5awyndg3dn5zlg7sq5hssgfatafk62kiiilapnqe")
 	TokenCarolDan_InvalidExpiredSealed = mustGetBundle(TokenCarolDan_InvalidExpiredCID).Sealed
 	TokenCarolDan_InvalidExpiredBundle = mustGetBundle(TokenCarolDan_InvalidExpiredCID)
 	TokenCarolDan_InvalidExpired       = mustGetBundle(TokenCarolDan_InvalidExpiredCID).Decoded
 )
 
 var (
-	TokenDanErin_InvalidExpiredCID    = cid.MustParse("bafyreifa265mung4nfpjjuiir5nytzgbrhfl66ye2dqmbq4p6dm7bzp4he")
+	TokenDanErin_InvalidExpiredCID    = cid.MustParse("bafyreihhnisabmkofuk3qaw37leijxqjaz5or6v2cufjxwzdkvuvv2dzbq")
 	TokenDanErin_InvalidExpiredSealed = mustGetBundle(TokenDanErin_InvalidExpiredCID).Sealed
 	TokenDanErin_InvalidExpiredBundle = mustGetBundle(TokenDanErin_InvalidExpiredCID)
 	TokenDanErin_InvalidExpired       = mustGetBundle(TokenDanErin_InvalidExpiredCID).Decoded
 )
 
 var (
-	TokenErinFrank_InvalidExpiredCID    = cid.MustParse("bafyreicde2per7ynjruvstuae67dxzdg2iepid3nonrmgr6tvodzpbqomu")
+	TokenErinFrank_InvalidExpiredCID    = cid.MustParse("bafyreigeokaziviwm5kzmkpwesj3gta5k7zrd62x4a746fnrnkhvatwbna")
 	TokenErinFrank_InvalidExpiredSealed = mustGetBundle(TokenErinFrank_InvalidExpiredCID).Sealed
 	TokenErinFrank_InvalidExpiredBundle = mustGetBundle(TokenErinFrank_InvalidExpiredCID)
 	TokenErinFrank_InvalidExpired       = mustGetBundle(TokenErinFrank_InvalidExpiredCID).Decoded

token/delegation/examples_test.go

@@ -41,8 +41,7 @@ func ExampleNew() {
 		)),
 	)
 
-	tkn, err := delegation.New(didtest.PersonaBob.DID(), didtest.PersonaCarol.DID(), cmd, pol,
+	tkn, err := delegation.New(didtest.PersonaBob.DID(), didtest.PersonaCarol.DID(), cmd, pol, didtest.PersonaAlice.DID(),
-		delegation.WithSubject(didtest.PersonaAlice.DID()),
 		delegation.WithExpirationIn(time.Hour),
 		delegation.WithNotBeforeIn(time.Minute),
 		delegation.WithMeta("foo", "bar"),

token/delegation/options.go

@@ -3,8 +3,6 @@ package delegation
 import (
 	"fmt"
 	"time"
-
-	"github.com/ucan-wg/go-ucan/did"
 )
 
 // Option is a type that allows optional fields to be set during the
@@ -85,20 +83,6 @@ func WithNotBeforeIn(nbf time.Duration) Option {
 	}
 }
 
-// WithSubject sets the Tokens's optional "subject" field to the value of
-// provided did.DID.
-//
-// This Option should only be used with the New constructor - since
-// Subject is a required parameter when creating a Token via the Root
-// constructor, any value provided via this Option will be silently
-// overwritten.
-func WithSubject(sub did.DID) Option {
-	return func(t *Token) error {
-		t.subject = sub
-		return nil
-	}
-}
-
 // WithNonce sets the Token's nonce with the given value.
 // If this option is not used, a random 12-byte nonce is generated for this required field.
 func WithNonce(nonce []byte) Option {

token/delegation/schema_test.go

@@ -33,9 +33,12 @@ func TestSchemaRoundTrip(t *testing.T) {
 		p1, err := delegation.FromDagJson(delegationJson)
 		require.NoError(t, err)
 
+		_, newCID, err := p1.ToSealed(privKey)
+		require.NoError(t, err)
+
 		cborBytes, id, err := p1.ToSealed(privKey)
 		require.NoError(t, err)
-		assert.Equal(t, newCID, envelope.CIDToBase58BTC(id))
+		assert.Equal(t, envelope.CIDToBase58BTC(newCID), envelope.CIDToBase58BTC(id))
 
 		p2, c2, err := delegation.FromSealed(cborBytes)
 		require.NoError(t, err)
@@ -58,10 +61,13 @@ func TestSchemaRoundTrip(t *testing.T) {
 		p1, err := delegation.FromDagJsonReader(buf)
 		require.NoError(t, err)
 
+		_, newCID, err := p1.ToSealed(privKey)
+		require.NoError(t, err)
+
 		cborBytes := &bytes.Buffer{}
 		id, err := p1.ToSealedWriter(cborBytes, privKey)
 		require.NoError(t, err)
-		assert.Equal(t, newCID, envelope.CIDToBase58BTC(id))
+		assert.Equal(t, envelope.CIDToBase58BTC(newCID), envelope.CIDToBase58BTC(id))
 
 		// buf = bytes.NewBuffer(cborBytes.Bytes())
 		p2, c2, err := delegation.FromSealedReader(cborBytes)

token/delegation/testdata/new.dagjson

@@ -1 +1 @@
-[{"/":{"bytes":"BBabgnWqd+cjwG1td0w9BudNocmUwoR89RMZTqZHk3osCXEI/bOkko0zTvlusaE4EMBBeSzZDKzjvunLBfdiBg"}},{"h":{"/":{"bytes":"NO0BcQ"}},"ucan/dlg@1.0.0-rc.1":{"aud":"did:key:z6MkvJPmEZZYbgiw1ouT1oouTsTFBHJSts9ophVsNgcRmYxU","cmd":"/foo/bar","exp":7258118400,"iss":"did:key:z6Mkuukk2skDXLQn7NK3Eh9jMndYfvDBxxktgpidJAqb7M3p","meta":{"bar":"barr","foo":"fooo"},"nonce":{"/":{"bytes":"NnJvRGhHaTBraU5yaVFBejdKM2QrYk9lb0kvdGo4RU5pa21RTmJ0am5EMA"}},"pol":[["==",".status","draft"],["all",".reviewer",["like",".email","*@example.com"]],["any",".tags",["or",[["==",".","news"],["==",".","press"]]]]],"sub":"did:key:z6Mkuukk2skDXLQn7NK3Eh9jMndYfvDBxxktgpidJAqb7M3p"}}]
+[{"/":{"bytes":"YJsl8EMLnXSFE/nKKjMxz9bHHo+Y7QeLEzukEzW1TB+m53TTiY1aOt+qUO8JaTcOKsOHt/a4Vn+YiOd5CkLdAQ"}},{"h":{"/":{"bytes":"NO0BcQ"}},"ucan/dlg@1.0.0-rc.1":{"aud":"did:key:z6MkvJPmEZZYbgiw1ouT1oouTsTFBHJSts9ophVsNgcRmYxU","cmd":"/foo/bar","exp":7258118400,"iss":"did:key:z6Mkuukk2skDXLQn7NK3Eh9jMndYfvDBxxktgpidJAqb7M3p","meta":{"bar":"barr","foo":"fooo"},"nonce":{"/":{"bytes":"NnJvRGhHaTBraU5yaVFBejdKM2QrYk9lb0kvdGo4RU5pa21RTmJ0am5EMA"}},"pol":[["==",".status","draft"],["all",".reviewer",["like",".email","*@example.com"]],["any",".tags",["or",[["==",".","news"],["==",".","press"]]]]],"sub":"did:key:z6Mkgupchh5HwuHahS7YsyE8bLua1Mr8p2iKNRhyvSvRAs9n"}}]

token/delegation/testdata/powerline.dagjson

@@ -0,0 +1 @@
+[{"/":{"bytes":"i3YkPDvNSU4V8XYEluZhLH0b+NDcW/6+PtPSUHC17cmXXqgelG0K4EzWQQkS9UsYCHfkZSCn9NjGSXYMMFhaAQ"}},{"h":{"/":{"bytes":"NO0BcQ"}},"ucan/dlg@1.0.0-rc.1":{"aud":"did:key:z6MkvJPmEZZYbgiw1ouT1oouTsTFBHJSts9ophVsNgcRmYxU","cmd":"/foo/bar","exp":7258118400,"iss":"did:key:z6Mkuukk2skDXLQn7NK3Eh9jMndYfvDBxxktgpidJAqb7M3p","meta":{"bar":"barr","foo":"fooo"},"nonce":{"/":{"bytes":"NnJvRGhHaTBraU5yaVFBejdKM2QrYk9lb0kvdGo4RU5pa21RTmJ0am5EMA"}},"pol":[["==",".status","draft"],["all",".reviewer",["like",".email","*@example.com"]],["any",".tags",["or",[["==",".","news"],["==",".","press"]]]]]}}]

token/invocation/examples_test.go

@@ -27,7 +27,7 @@ func ExampleNew() {
 		return
 	}
 
-	inv, err := invocation.New(iss, sub, cmd, prf,
+	inv, err := invocation.New(iss, cmd, sub, prf,
 		invocation.WithArgument("uri", args["uri"]),
 		invocation.WithArgument("headers", args["headers"]),
 		invocation.WithArgument("payload", args["payload"]),

token/invocation/invocation.go

@@ -8,8 +8,10 @@
 package invocation
 
 import (
+	"encoding/base64"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/ipfs/go-cid"
@@ -67,7 +69,9 @@ type Token struct {
 //
 // With the exception of the WithMeta option, all others will overwrite
 // the previous contents of their target field.
-func New(iss, sub did.DID, cmd command.Command, prf []cid.Cid, opts ...Option) (*Token, error) {
+//
+// You can read it as "(Issuer - I) executes (command) on (subject)".
+func New(iss did.DID, cmd command.Command, sub did.DID, prf []cid.Cid, opts ...Option) (*Token, error) {
 	iat := time.Now()
 
 	tkn := Token{
@@ -212,6 +216,24 @@ func (t *Token) IsValidAt(ti time.Time) bool {
 	return true
 }
 
+func (t *Token) String() string {
+	var res strings.Builder
+
+	res.WriteString(fmt.Sprintf("Issuer: %s\n", t.Issuer()))
+	res.WriteString(fmt.Sprintf("Audience: %s\n", t.Audience()))
+	res.WriteString(fmt.Sprintf("Subject: %v\n", t.Subject()))
+	res.WriteString(fmt.Sprintf("Command: %s\n", t.Command()))
+	res.WriteString(fmt.Sprintf("Args: %s\n", t.Arguments()))
+	res.WriteString(fmt.Sprintf("Proof: %v\n", t.Proof()))
+	res.WriteString(fmt.Sprintf("Nonce: %s\n", base64.StdEncoding.EncodeToString(t.Nonce())))
+	res.WriteString(fmt.Sprintf("Meta: %s\n", t.Meta()))
+	res.WriteString(fmt.Sprintf("Expiration: %v\n", t.Expiration()))
+	res.WriteString(fmt.Sprintf("Invoked At: %v\n", t.InvokedAt()))
+	res.WriteString(fmt.Sprintf("Cause: %v", t.Cause()))
+
+	return res.String()
+}
+
 func (t *Token) validate() error {
 	var errs error
 

token/invocation/invocation_test.go

@@ -129,7 +129,7 @@ func TestToken_ExecutionAllowed(t *testing.T) {
 		testFails(t, invocation.ErrWrongSub, didtest.PersonaFrank, delegationtest.ExpandedCommand, emptyArguments, delegationtest.ProofAliceBobCarolDanErinFrank_InvalidSubject)
 	})
 
-	t.Run("passes - arguments satify example policy", func(t *testing.T) {
+	t.Run("passes - arguments satisfy example policy", func(t *testing.T) {
 		t.Parallel()
 
 		testFails(t, invocation.ErrPolicyNotSatisfied, didtest.PersonaFrank, delegationtest.NominalCommand, policytest.SpecInvalidArguments, delegationtest.ProofAliceBobCarolDanErinFrank_ValidExamplePolicy)
@@ -142,7 +142,7 @@ func test(t *testing.T, persona didtest.Persona, cmd command.Command, args *args
 
 	opts = append(opts, invocation.WithArguments(args))
 
-	tkn, err := invocation.New(persona.DID(), didtest.PersonaAlice.DID(), cmd, prf, opts...)
+	tkn, err := invocation.New(persona.DID(), cmd, didtest.PersonaAlice.DID(), prf, opts...)
 	require.NoError(t, err)
 
 	return tkn.ExecutionAllowed(delegationtest.GetDelegationLoader())

token/invocation/ipld_test.go

@@ -16,7 +16,7 @@ func TestSealUnsealRoundtrip(t *testing.T) {
 	privKey, iss, sub, cmd, args, prf, meta, err := setupExampleNew()
 	require.NoError(t, err)
 
-	tkn1, err := invocation.New(iss, sub, cmd, prf,
+	tkn1, err := invocation.New(iss, cmd, sub, prf,
 		invocation.WithArgument("uri", args["uri"]),
 		invocation.WithArgument("headers", args["headers"]),
 		invocation.WithArgument("payload", args["payload"]),

token/invocation/options.go

@@ -38,11 +38,15 @@ func WithArguments(args *args.Args) Option {
 
 // WithAudience sets the Token's audience to the provided did.DID.
 //
+// This can be used if the resource on which the token operates on is different
+// from the subject. In that situation, the subject is akin to the "service" and
+// the audience is akin to the resource.
+//
 // If the provided did.DID is the same as the Token's subject, the
 // audience is not set.
 func WithAudience(aud did.DID) Option {
 	return func(t *Token) error {
-		if t.subject.String() != aud.String() {
+		if t.subject != aud {
 			t.audience = aud
 		}
 

token/invocation/proof.go

@@ -40,7 +40,7 @@ import (
 //     c. The first proof must be issued to the Invoker (audience DID).
 //     d. The Issuer of each delegation must be the Audience in the next one.
 //     e. The last token must be a root delegation.
-//     f. The Subject of each delegation must equal the invocation's Audience field.
+//     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.
 //
 //  5. If steps 1-4 pass:
@@ -58,18 +58,18 @@ func (t *Token) verifyProofs(delegations []*delegation.Token) error {
 
 	cmd := t.command
 	iss := t.issuer
-	aud := t.audience
+	sub := t.subject
-	if !aud.Defined() {
+	if t.audience.Defined() {
-		aud = t.subject
+		sub = t.audience
 	}
 
 	// control from the invocation to the root
 	for i, dlgCid := range t.proof {
 		dlg := delegations[i]
 
-		// The Subject of each delegation must equal the invocation's Audience field. - 4f
+		// The Subject of each delegation must equal the invocation's Subject (or Audience if defined). - 4f
-		if dlg.Subject() != aud {
+		if dlg.Subject() != sub {
-			return fmt.Errorf("%w: delegation %s, expected %s, got %s", ErrWrongSub, dlgCid, aud, dlg.Subject())
+			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