Pad non-padded secrets. This lets us continue building on <= go1.8.

- Add tests for secrets using various padding methods.
- Add a new method/test to append padding to non-padded secrets.

util_test.go

@@ -0,0 +1,53 @@
+package twofactor
+
+import (
+	"encoding/base32"
+	"fmt"
+	"math/rand"
+	"strings"
+	"testing"
+)
+
+const letters = "1234567890!@#$%^&*()abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func randString() string {
+	b := make([]byte, rand.Intn(len(letters)))
+	for i := range b {
+		b[i] = letters[rand.Intn(len(letters))]
+	}
+	return base32.StdEncoding.EncodeToString(b)
+}
+
+func TestPadding(t *testing.T) {
+	for i := 0; i < 300; i++ {
+		b := randString()
+		origEncoding := string(b)
+		modEncoding := strings.Replace(string(b), "=", "", -1)
+		str, err := base32.StdEncoding.DecodeString(origEncoding)
+		if err != nil {
+			fmt.Println("Can't decode: ", string(b))
+			t.FailNow()
+		}
+
+		paddedEncoding := Pad(modEncoding)
+		if origEncoding != paddedEncoding {
+			fmt.Println("Padding failed:")
+			fmt.Printf("Expected: '%s'", origEncoding)
+			fmt.Printf("Got: '%s'", paddedEncoding)
+			t.FailNow()
+		} else {
+			mstr, err := base32.StdEncoding.DecodeString(paddedEncoding)
+			if err != nil {
+				fmt.Println("Can't decode: ", paddedEncoding)
+				t.FailNow()
+			}
+
+			if string(mstr) != string(str) {
+				fmt.Println("Re-padding failed:")
+				fmt.Printf("Expected: '%s'", str)
+				fmt.Printf("Got: '%s'", mstr)
+				t.FailNow()
+			}
+		}
+	}
+}