feat: export unexpected audience error

oidc/verify.go

@@ -12,7 +12,7 @@ import (
 	"strings"
 	"time"
 
-	jose "github.com/go-jose/go-jose/v3"
+	"github.com/go-jose/go-jose/v3"
 	"golang.org/x/oauth2"
 )
 
@@ -33,6 +33,19 @@ func (e *TokenExpiredError) Error() string {
 	return fmt.Sprintf("oidc: token is expired (Token Expiry: %v)", e.Expiry)
 }
 
+// UnexpectedAudienceError indicates that the audience claim of the token did not match
+// any of the expected audiences.
+type UnexpectedAudienceError struct {
+	// ClientID is the client ID that was used to initialize the verifier.
+	ClientID string
+	// Audience is the audiences specified in the token.
+	Audience []string
+}
+
+func (e *UnexpectedAudienceError) Error() string {
+	return fmt.Sprintf("oidc: expected audience %q got %q", e.ClientID, e.Audience)
+}
+
 // KeySet is a set of publc JSON Web Keys that can be used to validate the signature
 // of JSON web tokens. This is expected to be backed by a remote key set through
 // provider metadata discovery or an in-memory set of keys delivered out-of-band.
@@ -274,7 +287,7 @@ func (v *IDTokenVerifier) Verify(ctx context.Context, rawIDToken string) (*IDTok
 	if !v.config.SkipClientIDCheck {
 		if v.config.ClientID != "" {
 			if !contains(t.Audience, v.config.ClientID) {
-				return nil, fmt.Errorf("oidc: expected audience %q got %q", v.config.ClientID, t.Audience)
+				return nil, &UnexpectedAudienceError{v.config.ClientID, t.Audience}
 			}
 		} else {
 			return nil, fmt.Errorf("oidc: invalid configuration, clientID must be provided or SkipClientIDCheck must be set")

oidc/verify_test.go

@@ -175,8 +175,8 @@ func TestVerifyAudience(t *testing.T) {
 				ClientID:        "client1",
 				SkipExpiryCheck: true,
 			},
-			signKey: newRSAKey(t),
-			wantErr: true,
+			signKey:    newRSAKey(t),
+			wantErrAud: true,
 		},
 		{
 			name:    "multiple audiences, one matches",
@@ -573,6 +573,7 @@ type verificationTest struct {
 	config        Config
 	wantErr       bool
 	wantErrExpiry bool
+	wantErrAud    bool
 }
 
 func (v verificationTest) runGetToken(t *testing.T) (*IDToken, error) {
@@ -605,10 +606,10 @@ func (v verificationTest) runGetToken(t *testing.T) (*IDToken, error) {
 
 func (v verificationTest) run(t *testing.T) {
 	_, err := v.runGetToken(t)
-	if err != nil && !v.wantErr && !v.wantErrExpiry {
+	if err != nil && !v.wantErr && !v.wantErrExpiry && !v.wantErrAud {
 		t.Errorf("%v", err)
 	}
-	if err == nil && (v.wantErr || v.wantErrExpiry) {
+	if err == nil && (v.wantErr || v.wantErrExpiry || v.wantErrAud) {
 		t.Errorf("expected error")
 	}
 	if v.wantErrExpiry {
@@ -617,4 +618,10 @@ func (v verificationTest) run(t *testing.T) {
 			t.Errorf("expected *TokenExpiryError but got %q", err)
 		}
 	}
+	if v.wantErrAud {
+		var errAud *UnexpectedAudienceError
+		if !errors.As(err, &errAud) {
+			t.Errorf("expected *AudienceError but got %q", err)
+		}
+	}
 }