Bring the sftp server code into the package itself

api/sftp_endpoints.go

@@ -2,11 +2,57 @@ package api
 
 import (
 	"encoding/json"
+	"github.com/apex/log"
 	"github.com/pkg/errors"
-	"github.com/pterodactyl/sftp-server"
+	"regexp"
 )
 
-func (r *PanelRequest) ValidateSftpCredentials(request sftp_server.AuthenticationRequest) (*sftp_server.AuthenticationResponse, error) {
+type SftpAuthRequest struct {
+	User          string `json:"username"`
+	Pass          string `json:"password"`
+	IP            string `json:"ip"`
+	SessionID     []byte `json:"session_id"`
+	ClientVersion []byte `json:"client_version"`
+}
+
+type SftpAuthResponse struct {
+	Server      string   `json:"server"`
+	Token       string   `json:"token"`
+	Permissions []string `json:"permissions"`
+}
+
+type sftpInvalidCredentialsError struct {
+}
+
+func (ice sftpInvalidCredentialsError) Error() string {
+	return "the credentials provided were invalid"
+}
+
+func IsInvalidCredentialsError(err error) bool {
+	_, ok := err.(*sftpInvalidCredentialsError)
+
+	return ok
+}
+
+// Usernames all follow the same format, so don't even bother hitting the API if the username is not
+// at least in the expected format. This is very basic protection against random bots finding the SFTP
+// server and sending a flood of usernames.
+var validUsernameRegexp = regexp.MustCompile(`^(?i)(.+)\.([a-z0-9]{8})$`)
+
+func (r *PanelRequest) ValidateSftpCredentials(request SftpAuthRequest) (*SftpAuthResponse, error) {
+	// If the username doesn't meet the expected format that the Panel would even recognize just go ahead
+	// and bail out of the process here to avoid accidentially brute forcing the panel if a bot decides
+	// to connect to spam username attempts.
+	if !validUsernameRegexp.MatchString(request.User) {
+		log.WithFields(log.Fields{
+			"subsystem": "sftp",
+			"username": request.User,
+			"ip": request.IP,
+		}).Warn("failed to validate user credentials (invalid format)")
+
+		return nil, new(sftpInvalidCredentialsError)
+	}
+
 	b, err := json.Marshal(request)
 	if err != nil {
 		return nil, err
@@ -22,7 +68,7 @@ func (r *PanelRequest) ValidateSftpCredentials(request sftp_server.Authenticatio
 
 	if r.HasError() {
 		if r.HttpResponseCode() >= 400 && r.HttpResponseCode() < 500 {
-			return nil, new(sftp_server.InvalidCredentialsError)
+			return nil, new(sftpInvalidCredentialsError)
 		}
 
 		rerr := errors.New(r.Error().String())
@@ -30,7 +76,7 @@ func (r *PanelRequest) ValidateSftpCredentials(request sftp_server.Authenticatio
 		return nil, rerr
 	}
 
-	response := new(sftp_server.AuthenticationResponse)
+	response := new(SftpAuthResponse)
 	body, _ := r.ReadBody()
 
 	if err := json.Unmarshal(body, response); err != nil {