introduce the password reminder infrastructure

util/random.go

@@ -11,8 +11,9 @@
 package util
 
 import (
-	"crypto/rand"
+	crand "crypto/rand"
 	"io"
+	mrand "math/rand"
 )
 
 // authAlphabet is the set of characters from which we generate auth strings.
@@ -24,7 +25,7 @@ const authStringLen = 32
 // GenerateRandomAuthString generates a random authentication string.
 func GenerateRandomAuthString() string {
 	b := make([]byte, authStringLen)
-	if _, err := io.ReadFull(rand.Reader, b); err != nil {
+	if _, err := io.ReadFull(crand.Reader, b); err != nil {
 		// can't happen (at least on a modern OS)
 		panic("failed to read random: " + err.Error())
 	}
@@ -33,3 +34,8 @@ func GenerateRandomAuthString() string {
 	}
 	return string(b)
 }
+
+// GenerateRandomConfirmationNumber generates a random 7-digit confirmation number.
+func GenerateRandomConfirmationNumber() int32 {
+	return mrand.Int31n(9000000) + 1000000
+}