[feature] add TOTP two-factor authentication (2FA) (#3960)

* [feature] add TOTP two-factor authentication (2FA)

* use byteutil.S2B to avoid allocations when comparing + generating password hashes

* don't bother with string conversion  for consts

* use io.ReadFull

* use MustGenerateSecret for backup codes

* rename util functions

vendor/github.com/boombuler/barcode/utils/base1dcode.go

@@ -0,0 +1,57 @@
+// Package utils contain some utilities which are needed to create barcodes
+package utils
+
+import (
+	"image"
+	"image/color"
+
+	"github.com/boombuler/barcode"
+)
+
+type base1DCode struct {
+	*BitList
+	kind    string
+	content string
+}
+
+type base1DCodeIntCS struct {
+	base1DCode
+	checksum int
+}
+
+func (c *base1DCode) Content() string {
+	return c.content
+}
+
+func (c *base1DCode) Metadata() barcode.Metadata {
+	return barcode.Metadata{c.kind, 1}
+}
+
+func (c *base1DCode) ColorModel() color.Model {
+	return color.Gray16Model
+}
+
+func (c *base1DCode) Bounds() image.Rectangle {
+	return image.Rect(0, 0, c.Len(), 1)
+}
+
+func (c *base1DCode) At(x, y int) color.Color {
+	if c.GetBit(x) {
+		return color.Black
+	}
+	return color.White
+}
+
+func (c *base1DCodeIntCS) CheckSum() int {
+	return c.checksum
+}
+
+// New1DCodeIntCheckSum creates a new 1D barcode where the bars are represented by the bits in the bars BitList
+func New1DCodeIntCheckSum(codeKind, content string, bars *BitList, checksum int) barcode.BarcodeIntCS {
+	return &base1DCodeIntCS{base1DCode{bars, codeKind, content}, checksum}
+}
+
+// New1DCode creates a new 1D barcode where the bars are represented by the bits in the bars BitList
+func New1DCode(codeKind, content string, bars *BitList) barcode.Barcode {
+	return &base1DCode{bars, codeKind, content}
+}