Add SetSessionGatekeeper

This allows you to define a function which determines whether a session connection (either incoming or outgoing) is allowed based on the public key.

src/yggdrasil/api.go

@@ -395,6 +395,18 @@ func (c *Core) GetNodeInfo(keyString, coordString string, nocache bool) (NodeInf
 	return NodeInfoPayload{}, errors.New(fmt.Sprintf("getNodeInfo timeout: %s", keyString))
 }
 
+// SetSessionGatekeeper allows you to configure a handler function for deciding
+// whether a session should be allowed or not. The default session firewall is
+// implemented in this way. The function receives the public key of the remote
+// side, and a boolean which is true if we initiated the session or false if we
+// received an incoming session request.
+func (c *Core) SetSessionGatekeeper(f func(pubkey *crypto.BoxPubKey, initiator bool) bool) {
+	c.sessions.isAllowedMutex.Lock()
+	defer c.sessions.isAllowedMutex.Unlock()
+
+	c.sessions.isAllowedHandler = f
+}
+
 // SetLogger sets the output logger of the Yggdrasil node after startup. This
 // may be useful if you want to redirect the output later.
 func (c *Core) SetLogger(log *log.Logger) {