add password generator

Signed-off-by: Christian Richter <crichter@owncloud.com>

ocis-pkg/generators/password.go

@@ -0,0 +1,20 @@
+package generators
+
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+func GenerateRandomPassword(length int) (string, error) {
+	const chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-=+!@#$%^&*."
+	ret := make([]byte, length)
+	for i := 0; i < length; i++ {
+		num, err := rand.Int(rand.Reader, big.NewInt(int64(len(chars))))
+		if err != nil {
+			return "", err
+		}
+		ret[i] = chars[num.Int64()]
+	}
+
+	return string(ret), nil
+}