Add filtering by GCP Project ID.

Fixes smallstep/step#155

authority/provisioner/gcp.go

@@ -70,6 +70,7 @@ type GCP struct {
 	Type                   string   `json:"type"`
 	Name                   string   `json:"name"`
 	ServiceAccounts        []string `json:"serviceAccounts"`
+	ProjectIDs             []string `json:"projectIDs"`
 	DisableCustomSANs      bool     `json:"disableCustomSANs"`
 	DisableTrustOnFirstUse bool     `json:"disableTrustOnFirstUse"`
 	Claims                 *Claims  `json:"claims,omitempty"`
@@ -284,6 +285,20 @@ func (p *GCP) authorizeToken(token string) (*gcpPayload, error) {
 		}
 	}
 
+	// validate projects
+	if len(p.ProjectIDs) > 0 {
+		var found bool
+		for _, pi := range p.ProjectIDs {
+			if pi == claims.Google.ComputeEngine.ProjectID {
+				found = true
+				break
+			}
+		}
+		if !found {
+			return nil, errors.New("invalid token: invalid project id")
+		}
+	}
+
 	switch {
 	case claims.Google.ComputeEngine.InstanceID == "":
 		return nil, errors.New("token google.compute_engine.instance_id cannot be empty")

authority/provisioner/gcp_test.go

@@ -203,6 +203,10 @@ func TestGCP_AuthorizeSign(t *testing.T) {
 	assert.FatalError(t, err)
 	p2.DisableCustomSANs = true
 
+	p3, err := generateGCP()
+	assert.FatalError(t, err)
+	p3.ProjectIDs = []string{"other-project-id"}
+
 	aKey, err := generateJSONWebKey()
 	assert.FatalError(t, err)
 
@@ -216,6 +220,11 @@ func TestGCP_AuthorizeSign(t *testing.T) {
 		"instance-id", "instance-name", "project-id", "zone",
 		time.Now(), &p2.keyStore.keySet.Keys[0])
 	assert.FatalError(t, err)
+	t3, err := generateGCPToken(p3.ServiceAccounts[0],
+		"https://accounts.google.com", p3.GetID(),
+		"instance-id", "instance-name", "other-project-id", "zone",
+		time.Now(), &p3.keyStore.keySet.Keys[0])
+	assert.FatalError(t, err)
 
 	failKey, err := generateGCPToken(p1.ServiceAccounts[0],
 		"https://accounts.google.com", p1.GetID(),
@@ -247,6 +256,11 @@ func TestGCP_AuthorizeSign(t *testing.T) {
 		"instance-id", "instance-name", "project-id", "zone",
 		time.Now(), &p1.keyStore.keySet.Keys[0])
 	assert.FatalError(t, err)
+	failInvalidProjectID, err := generateGCPToken(p3.ServiceAccounts[0],
+		"https://accounts.google.com", p3.GetID(),
+		"instance-id", "instance-name", "project-id", "zone",
+		time.Now(), &p3.keyStore.keySet.Keys[0])
+	assert.FatalError(t, err)
 	failInstanceID, err := generateGCPToken(p1.ServiceAccounts[0],
 		"https://accounts.google.com", p1.GetID(),
 		"", "instance-name", "project-id", "zone",
@@ -280,6 +294,7 @@ func TestGCP_AuthorizeSign(t *testing.T) {
 	}{
 		{"ok", p1, args{t1}, 4, false},
 		{"ok", p2, args{t2}, 5, false},
+		{"ok", p3, args{t3}, 4, false},
 		{"fail token", p1, args{"token"}, 0, true},
 		{"fail key", p1, args{failKey}, 0, true},
 		{"fail iss", p1, args{failIss}, 0, true},
@@ -287,6 +302,7 @@ func TestGCP_AuthorizeSign(t *testing.T) {
 		{"fail exp", p1, args{failExp}, 0, true},
 		{"fail nbf", p1, args{failNbf}, 0, true},
 		{"fail service account", p1, args{failServiceAccount}, 0, true},
+		{"fail invalid project id", p3, args{failInvalidProjectID}, 0, true},
 		{"fail instance id", p1, args{failInstanceID}, 0, true},
 		{"fail instance name", p1, args{failInstanceName}, 0, true},
 		{"fail project id", p1, args{failProjectID}, 0, true},