add support for auth plugins

sdk/plugin/auth/auth.go

@@ -0,0 +1,59 @@
+// Package auth defines the implementation for authentication plugins.
+// Authentication plugins allow to authenticate external users
+package auth
+
+import (
+	"context"
+
+	"github.com/hashicorp/go-plugin"
+	"google.golang.org/grpc"
+
+	"github.com/drakkan/sftpgo/v2/sdk/plugin/auth/proto"
+)
+
+const (
+	// PluginName defines the name for a notifier plugin
+	PluginName = "auth"
+)
+
+// Handshake is a common handshake that is shared by plugin and host.
+var Handshake = plugin.HandshakeConfig{
+	ProtocolVersion:  1,
+	MagicCookieKey:   "SFTPGO_AUTH_PLUGIN",
+	MagicCookieValue: "d1ed507d-d2be-4a38-a460-6fe0b2cc7efc",
+}
+
+// PluginMap is the map of plugins we can dispense.
+var PluginMap = map[string]plugin.Plugin{
+	PluginName: &Plugin{},
+}
+
+// Authenticator defines the interface for authentication plugins
+type Authenticator interface {
+	CheckUserAndPass(username, password, ip, protocol string, userAsJSON []byte) ([]byte, error)
+	CheckUserAndTLSCert(username, tlsCert, ip, protocol string, userAsJSON []byte) ([]byte, error)
+	CheckUserAndPublicKey(username, pubKey, ip, protocol string, userAsJSON []byte) ([]byte, error)
+	CheckUserAndKeyboardInteractive(username, ip, protocol string, userAsJSON []byte) ([]byte, error)
+	SendKeyboardAuthRequest(requestID, username, password, ip string, answers, questions []string, step int32) (string, []string, []bool, int, int, error)
+}
+
+// Plugin defines the implementation to serve/connect to an authe plugin
+type Plugin struct {
+	plugin.Plugin
+	Impl Authenticator
+}
+
+// GRPCServer defines the GRPC server implementation for this plugin
+func (p *Plugin) GRPCServer(broker *plugin.GRPCBroker, s *grpc.Server) error {
+	proto.RegisterAuthServer(s, &GRPCServer{
+		Impl: p.Impl,
+	})
+	return nil
+}
+
+// GRPCClient defines the GRPC client implementation for this plugin
+func (p *Plugin) GRPCClient(ctx context.Context, broker *plugin.GRPCBroker, c *grpc.ClientConn) (interface{}, error) {
+	return &GRPCClient{
+		client: proto.NewAuthClient(c),
+	}, nil
+}