add a GetConfigForClient callback to the Config

interface.go

@@ -239,6 +239,9 @@ type ConnectionIDGenerator interface {
 
 // Config contains all configuration data needed for a QUIC server or client.
 type Config struct {
+	// GetConfigForClient is called for incoming connections.
+	// If the error is not nil, the connection attempt is refused.
+	GetConfigForClient func(info *ClientHelloInfo) (*Config, error)
 	// The QUIC versions that can be negotiated.
 	// If not set, it uses all versions available.
 	Versions []VersionNumber
@@ -324,6 +327,10 @@ type Config struct {
 	Tracer          logging.Tracer
 }
 
+type ClientHelloInfo struct {
+	RemoteAddr net.Addr
+}
+
 // ConnectionState records basic details about a QUIC connection
 type ConnectionState struct {
 	TLS               handshake.ConnectionState