[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/scaledbarcode.go

@@ -0,0 +1,134 @@
+package barcode
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"image/color"
+	"math"
+)
+
+type wrapFunc func(x, y int) color.Color
+
+type scaledBarcode struct {
+	wrapped     Barcode
+	wrapperFunc wrapFunc
+	rect        image.Rectangle
+}
+
+type intCSscaledBC struct {
+	scaledBarcode
+}
+
+func (bc *scaledBarcode) Content() string {
+	return bc.wrapped.Content()
+}
+
+func (bc *scaledBarcode) Metadata() Metadata {
+	return bc.wrapped.Metadata()
+}
+
+func (bc *scaledBarcode) ColorModel() color.Model {
+	return bc.wrapped.ColorModel()
+}
+
+func (bc *scaledBarcode) Bounds() image.Rectangle {
+	return bc.rect
+}
+
+func (bc *scaledBarcode) At(x, y int) color.Color {
+	return bc.wrapperFunc(x, y)
+}
+
+func (bc *intCSscaledBC) CheckSum() int {
+	if cs, ok := bc.wrapped.(BarcodeIntCS); ok {
+		return cs.CheckSum()
+	}
+	return 0
+}
+
+// Scale returns a resized barcode with the given width and height.
+func Scale(bc Barcode, width, height int) (Barcode, error) {
+	switch bc.Metadata().Dimensions {
+	case 1:
+		return scale1DCode(bc, width, height)
+	case 2:
+		return scale2DCode(bc, width, height)
+	}
+
+	return nil, errors.New("unsupported barcode format")
+}
+
+func newScaledBC(wrapped Barcode, wrapperFunc wrapFunc, rect image.Rectangle) Barcode {
+	result := &scaledBarcode{
+		wrapped:     wrapped,
+		wrapperFunc: wrapperFunc,
+		rect:        rect,
+	}
+
+	if _, ok := wrapped.(BarcodeIntCS); ok {
+		return &intCSscaledBC{*result}
+	}
+	return result
+}
+
+func scale2DCode(bc Barcode, width, height int) (Barcode, error) {
+	orgBounds := bc.Bounds()
+	orgWidth := orgBounds.Max.X - orgBounds.Min.X
+	orgHeight := orgBounds.Max.Y - orgBounds.Min.Y
+
+	factor := int(math.Min(float64(width)/float64(orgWidth), float64(height)/float64(orgHeight)))
+	if factor <= 0 {
+		return nil, fmt.Errorf("can not scale barcode to an image smaller than %dx%d", orgWidth, orgHeight)
+	}
+
+	offsetX := (width - (orgWidth * factor)) / 2
+	offsetY := (height - (orgHeight * factor)) / 2
+
+	wrap := func(x, y int) color.Color {
+		if x < offsetX || y < offsetY {
+			return color.White
+		}
+		x = (x - offsetX) / factor
+		y = (y - offsetY) / factor
+		if x >= orgWidth || y >= orgHeight {
+			return color.White
+		}
+		return bc.At(x, y)
+	}
+
+	return newScaledBC(
+		bc,
+		wrap,
+		image.Rect(0, 0, width, height),
+	), nil
+}
+
+func scale1DCode(bc Barcode, width, height int) (Barcode, error) {
+	orgBounds := bc.Bounds()
+	orgWidth := orgBounds.Max.X - orgBounds.Min.X
+	factor := int(float64(width) / float64(orgWidth))
+
+	if factor <= 0 {
+		return nil, fmt.Errorf("can not scale barcode to an image smaller than %dx1", orgWidth)
+	}
+	offsetX := (width - (orgWidth * factor)) / 2
+
+	wrap := func(x, y int) color.Color {
+		if x < offsetX {
+			return color.White
+		}
+		x = (x - offsetX) / factor
+
+		if x >= orgWidth {
+			return color.White
+		}
+		return bc.At(x, 0)
+	}
+
+	return newScaledBC(
+		bc,
+		wrap,
+		image.Rect(0, 0, width, height),
+	), nil
+}