Add ExternalCAs to swarm spec

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

types/swarm/swarm.go

@@ -54,6 +54,20 @@ type DispatcherConfig struct {
 // CAConfig represents CA configuration.
 type CAConfig struct {
 	NodeCertExpiry time.Duration `json:",omitempty"`
+	ExternalCAs    []*ExternalCA `json:",omitempty"`
+}
+
+// ExternalCAProtocol represents type of external CA.
+type ExternalCAProtocol string
+
+// ExternalCAProtocolCFSSL CFSSL
+const ExternalCAProtocolCFSSL ExternalCAProtocol = "cfssl"
+
+// ExternalCA defines external CA to be used by the cluster.
+type ExternalCA struct {
+	Protocol ExternalCAProtocol
+	URL      string
+	Options  map[string]string `json:",omitempty"`
 }
 
 // InitRequest is the request used to init a swarm.