Move username/password validation to Storage class

src/util.cr

@@ -101,3 +101,22 @@ def redirect(env, path)
   base = Config.current.base_url
   env.redirect File.join base, path
 end
+
+def validate_username(username)
+  if username.size < 3
+    raise "Username should contain at least 3 characters"
+  end
+  if (username =~ /^[A-Za-z0-9_]+$/).nil?
+    raise "Username should contain alphanumeric characters " \
+          "and underscores only"
+  end
+end
+
+def validate_password(password)
+  if password.size < 6
+    raise "Password should contain at least 6 characters"
+  end
+  if (password =~ /^[[:ascii:]]+$/).nil?
+    raise "password should contain ASCII characters only"
+  end
+end