random: stop using deprecated rand.Seed in go1.20 and later

lib/random/random.go

@@ -67,19 +67,3 @@ func Password(bits int) (password string, err error) {
 	password = base64.RawURLEncoding.EncodeToString(pw)
 	return password, nil
 }
-
-// Seed the global math/rand with crypto strong data
-//
-// This doesn't make it OK to use math/rand in crypto sensitive
-// environments - don't do that! However it does help to mitigate the
-// problem if that happens accidentally. This would have helped with
-// CVE-2020-28924 - #4783
-func Seed() error {
-	var seed int64
-	err := binary.Read(cryptorand.Reader, binary.LittleEndian, &seed)
-	if err != nil {
-		return fmt.Errorf("failed to read random seed: %w", err)
-	}
-	mathrand.Seed(seed)
-	return nil
-}

lib/random/random_seed.go

@@ -0,0 +1,17 @@
+//go:build go1.20
+
+package random
+
+// Seed the global math/rand with crypto strong data
+//
+// This doesn't make it OK to use math/rand in crypto sensitive
+// environments - don't do that! However it does help to mitigate the
+// problem if that happens accidentally. This would have helped with
+// CVE-2020-28924 - #4783
+//
+// As of Go 1.20 there is no reason to call math/rand.Seed with a
+// random value as it is self seeded to a random 64 bit number so this
+// does nothing.
+func Seed() error {
+	return nil
+}

lib/random/random_seed_old.go

@@ -0,0 +1,29 @@
+//go:build !go1.20
+
+package random
+
+import (
+	cryptorand "crypto/rand"
+	"encoding/binary"
+	"fmt"
+	mathrand "math/rand"
+)
+
+// Seed the global math/rand with crypto strong data
+//
+// This doesn't make it OK to use math/rand in crypto sensitive
+// environments - don't do that! However it does help to mitigate the
+// problem if that happens accidentally. This would have helped with
+// CVE-2020-28924 - #4783
+//
+// As of Go 1.20 there is no reason to call math/rand.Seed with a
+// random value as it is self seeded to a random 64 bit number.
+func Seed() error {
+	var seed int64
+	err := binary.Read(cryptorand.Reader, binary.LittleEndian, &seed)
+	if err != nil {
+		return fmt.Errorf("failed to read random seed: %w", err)
+	}
+	mathrand.Seed(seed)
+	return nil
+}