diff --git a/pkg/custom_detectors/custom_detectors.go b/pkg/custom_detectors/custom_detectors.go
index a54a070c5..36454e74e 100644
--- a/pkg/custom_detectors/custom_detectors.go
+++ b/pkg/custom_detectors/custom_detectors.go
@@ -46,9 +46,10 @@ type ropcTokenSource struct {
 	password      string
 	clientID      string
 	clientSecret  string
+	scope         string
 
-	mu    sync.Mutex
-	token string
+	mu     sync.Mutex
+	token  string
 	expiry time.Time
 }
 
@@ -60,6 +61,7 @@ func newROPCTokenSource(auth *custom_detectorspb.VerifierAuth, ropc *custom_dete
 		password:      ropc.GetPassword(),
 		clientID:      ropc.GetClientId(),
 		clientSecret:  ropc.GetClientSecret(),
+		scope:         ropc.GetScope(),
 	}
 }
 
@@ -81,12 +83,23 @@ func (s *ropcTokenSource) Token(ctx context.Context) (string, error) {
 	}
 
 	// POST form-encoded ROPC body per RFC 6749 Section 4.3.2.
+	// Only username, password, and grant_type are required.
+	// client_id and client_secret are conditional: included only when
+	// configured, supporting both public clients (no secret) and
+	// servers that use HTTP Basic auth for client authentication.
 	form := url.Values{
-		"grant_type":    {"password"},
-		"username":      {s.username},
-		"password":      {s.password},
-		"client_id":     {s.clientID},
-		"client_secret": {s.clientSecret},
+		"grant_type": {"password"},
+		"username":   {s.username},
+		"password":   {s.password},
+	}
+	if s.clientID != "" {
+		form.Set("client_id", s.clientID)
+	}
+	if s.clientSecret != "" {
+		form.Set("client_secret", s.clientSecret)
+	}
+	if s.scope != "" {
+		form.Set("scope", s.scope)
 	}
 
 	req, err := http.NewRequestWithContext(ctx, "POST", s.tokenEndpoint, strings.NewReader(form.Encode()))
diff --git a/pkg/pb/custom_detectorspb/custom_detectors.pb.go b/pkg/pb/custom_detectorspb/custom_detectors.pb.go
index 257d4885d..f253aad77 100644
--- a/pkg/pb/custom_detectorspb/custom_detectors.pb.go
+++ b/pkg/pb/custom_detectorspb/custom_detectors.pb.go
@@ -374,6 +374,10 @@ type ROPCConfig struct {
 	Password     string `protobuf:"bytes,2,opt,name=password,proto3" json:"password,omitempty"`
 	ClientId     string `protobuf:"bytes,3,opt,name=client_id,json=clientId,proto3" json:"client_id,omitempty"`
 	ClientSecret string `protobuf:"bytes,4,opt,name=client_secret,json=clientSecret,proto3" json:"client_secret,omitempty"`
+	// Optional OAuth2 scope(s) to request, space-delimited per RFC 6749
+	// Section 3.3. Some IdPs require a scope to issue tokens with the
+	// correct audience or permissions.
+	Scope string `protobuf:"bytes,5,opt,name=scope,proto3" json:"scope,omitempty"`
 }
 
 func (x *ROPCConfig) Reset() {
@@ -436,6 +440,13 @@ func (x *ROPCConfig) GetClientSecret() string {
 	return ""
 }
 
+func (x *ROPCConfig) GetScope() string {
+	if x != nil {
+		return x.Scope
+	}
+	return ""
+}
+
 type ValidationConfig struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -583,7 +594,7 @@ var file_custom_detectors_proto_rawDesc = []byte{
 	0x70, 0x63, 0x18, 0x02, 0x20, 0x01, 0x28, 0x0b, 0x32, 0x1c, 0x2e, 0x63, 0x75, 0x73, 0x74, 0x6f,
 	0x6d, 0x5f, 0x64, 0x65, 0x74, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x73, 0x2e, 0x52, 0x4f, 0x50, 0x43,
 	0x43, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x48, 0x00, 0x52, 0x04, 0x72, 0x6f, 0x70, 0x63, 0x42, 0x0e,
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+	0x0a, 0x0c, 0x67, 0x72, 0x61, 0x6e, 0x74, 0x5f, 0x63, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x22, 0x9c,
 	0x01, 0x0a, 0x0a, 0x52, 0x4f, 0x50, 0x43, 0x43, 0x6f, 0x6e, 0x66, 0x69, 0x67, 0x12, 0x1a, 0x0a,
 	0x08, 0x75, 0x73, 0x65, 0x72, 0x6e, 0x61, 0x6d, 0x65, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x52,
 	0x08, 0x75, 0x73, 0x65, 0x72, 0x6e, 0x61, 0x6d, 0x65, 0x12, 0x1a, 0x0a, 0x08, 0x70, 0x61, 0x73,
@@ -592,25 +603,26 @@ var file_custom_detectors_proto_rawDesc = []byte{
 	0x69, 0x64, 0x18, 0x03, 0x20, 0x01, 0x28, 0x09, 0x52, 0x08, 0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74,
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+	0x62, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/pkg/pb/custom_detectorspb/custom_detectors.pb.validate.go b/pkg/pb/custom_detectorspb/custom_detectors.pb.validate.go
index 1b3c86bc9..0f45ac593 100644
--- a/pkg/pb/custom_detectorspb/custom_detectors.pb.validate.go
+++ b/pkg/pb/custom_detectorspb/custom_detectors.pb.validate.go
@@ -678,6 +678,8 @@ func (m *ROPCConfig) validate(all bool) error {
 
 	// no validation rules for ClientSecret
 
+	// no validation rules for Scope
+
 	if len(errors) > 0 {
 		return ROPCConfigMultiError(errors)
 	}
diff --git a/proto/custom_detectors.proto b/proto/custom_detectors.proto
index f72733b0d..bd4d1c3db 100644
--- a/proto/custom_detectors.proto
+++ b/proto/custom_detectors.proto
@@ -56,6 +56,10 @@ message ROPCConfig {
   string password = 2;
   string client_id = 3;
   string client_secret = 4;
+  // Optional OAuth2 scope(s) to request, space-delimited per RFC 6749
+  // Section 3.3. Some IdPs require a scope to issue tokens with the
+  // correct audience or permissions.
+  string scope = 5;
 }
 
 message ValidationConfig {