Add TOTP MFA (#342)

internal/auth/totp/totp.go

@@ -0,0 +1,61 @@
+package totp
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/base64"
+	"github.com/pquerna/otp/totp"
+	"html/template"
+	"image/png"
+	"strings"
+)
+
+const secretSize = 16
+
+func GenerateQRCode(username, siteUrl string, secret []byte) (string, template.URL, error, []byte) {
+	var err error
+	if secret == nil {
+		secret, err = generateSecret()
+		if err != nil {
+			return "", "", err, nil
+		}
+	}
+
+	otpKey, err := totp.Generate(totp.GenerateOpts{
+		SecretSize:  secretSize,
+		Issuer:      "Opengist (" + strings.ReplaceAll(siteUrl, ":", "") + ")",
+		AccountName: username,
+		Secret:      secret,
+	})
+	if err != nil {
+		return "", "", err, nil
+	}
+
+	qrcode, err := otpKey.Image(320, 240)
+	if err != nil {
+		return "", "", err, nil
+	}
+
+	var imgBytes bytes.Buffer
+	if err = png.Encode(&imgBytes, qrcode); err != nil {
+		return "", "", err, nil
+	}
+
+	qrcodeImage := template.URL("data:image/png;base64," + base64.StdEncoding.EncodeToString(imgBytes.Bytes()))
+
+	return otpKey.Secret(), qrcodeImage, nil, secret
+}
+
+func Validate(passcode, secret string) bool {
+	return totp.Validate(passcode, secret)
+}
+
+func generateSecret() ([]byte, error) {
+	secret := make([]byte, secretSize)
+	_, err := rand.Reader.Read(secret)
+	if err != nil {
+		return nil, err
+	}
+
+	return secret, nil
+}