Two factor authentication support (#630)

* Initial commit for 2FA support

Signed-off-by: Andrew <write@imaginarycode.com>

* Add vendored files

* Add missing depends

* A few clean ups

* Added improvements, proper encryption

* Better encryption key

* Simplify "key" generation

* Make 2FA enrollment page more robust

* Fix typo

* Rename twofa/2FA to TwoFactor

* UNIQUE INDEX -> UNIQUE

vendor/github.com/boombuler/barcode/qr/alphanumeric.go

@@ -0,0 +1,66 @@
+package qr
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/boombuler/barcode/utils"
+)
+
+const charSet string = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:"
+
+func stringToAlphaIdx(content string) <-chan int {
+	result := make(chan int)
+	go func() {
+		for _, r := range content {
+			idx := strings.IndexRune(charSet, r)
+			result <- idx
+			if idx < 0 {
+				break
+			}
+		}
+		close(result)
+	}()
+
+	return result
+}
+
+func encodeAlphaNumeric(content string, ecl ErrorCorrectionLevel) (*utils.BitList, *versionInfo, error) {
+
+	contentLenIsOdd := len(content)%2 == 1
+	contentBitCount := (len(content) / 2) * 11
+	if contentLenIsOdd {
+		contentBitCount += 6
+	}
+	vi := findSmallestVersionInfo(ecl, alphaNumericMode, contentBitCount)
+	if vi == nil {
+		return nil, nil, errors.New("To much data to encode")
+	}
+
+	res := new(utils.BitList)
+	res.AddBits(int(alphaNumericMode), 4)
+	res.AddBits(len(content), vi.charCountBits(alphaNumericMode))
+
+	encoder := stringToAlphaIdx(content)
+
+	for idx := 0; idx < len(content)/2; idx++ {
+		c1 := <-encoder
+		c2 := <-encoder
+		if c1 < 0 || c2 < 0 {
+			return nil, nil, fmt.Errorf("\"%s\" can not be encoded as %s", content, AlphaNumeric)
+		}
+		res.AddBits(c1*45+c2, 11)
+	}
+	if contentLenIsOdd {
+		c := <-encoder
+		if c < 0 {
+			return nil, nil, fmt.Errorf("\"%s\" can not be encoded as %s", content, AlphaNumeric)
+		}
+		res.AddBits(c, 6)
+	}
+
+	addPaddingAndTerminator(res, vi)
+
+	return res, vi, nil
+}