mvp shell

backend/internal/authcode/authcode.go

@@ -0,0 +1,62 @@
+// Package authcode generates human-typeable, high-entropy invite/login codes.
+package authcode
+
+import (
+	"crypto/rand"
+	"math/big"
+	"strings"
+)
+
+// Crockford base32 alphabet (no I, L, O, U — avoids ambiguity for non-technical users).
+const alphabet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
+
+// groups x size = number of significant characters. 12 chars of base32 ≈ 60 bits of entropy.
+const (
+	groups    = 3
+	groupSize = 4
+)
+
+// New returns a fresh code formatted as XXXX-XXXX-XXXX using crypto/rand.
+func New() string {
+	var sb strings.Builder
+	sb.Grow(groups*groupSize + (groups - 1))
+	for g := 0; g < groups; g++ {
+		if g > 0 {
+			sb.WriteByte('-')
+		}
+		for i := 0; i < groupSize; i++ {
+			sb.WriteByte(alphabet[randIndex(len(alphabet))])
+		}
+	}
+	return sb.String()
+}
+
+// Normalize upper-cases, strips separators/whitespace, and maps Crockford's
+// interchangeable characters (I/L→1, O→0) so user-entered codes match storage.
+func Normalize(s string) string {
+	var sb strings.Builder
+	for _, r := range strings.ToUpper(strings.TrimSpace(s)) {
+		switch r {
+		case '-', ' ', '\t':
+			continue
+		case 'I', 'L':
+			sb.WriteRune('1')
+		case 'O':
+			sb.WriteRune('0')
+		case 'U':
+			sb.WriteRune('V')
+		default:
+			sb.WriteRune(r)
+		}
+	}
+	return sb.String()
+}
+
+func randIndex(n int) int {
+	v, err := rand.Int(rand.Reader, big.NewInt(int64(n)))
+	if err != nil {
+		// crypto/rand should never fail; if it does, fail loudly rather than emit a weak code.
+		panic("authcode: crypto/rand failure: " + err.Error())
+	}
+	return int(v.Int64())
+}