refactor: switch to use SecureRandom for random strings

app/models/concerns/has_authentication.rb

@@ -30,7 +30,7 @@ module HasAuthentication
   end
 
   def begin_password_reset(return_to = nil)
-    self.password_reset_token = Nifty::Utils::RandomString.generate(length: 24)
+    self.password_reset_token = SecureRandom.alphanumeric(24)
     self.password_reset_token_valid_until = 1.day.from_now
     save!
     AppMailer.password_reset(self, return_to).deliver

app/models/domain.rb

@@ -164,7 +164,7 @@ class Domain < ApplicationRecord
     return unless verification_method_changed?
 
     if verification_method == "DNS"
-      self.verification_token = Nifty::Utils::RandomString.generate(length: 32)
+      self.verification_token = SecureRandom.alphanumeric(32)
     elsif verification_method == "Email"
       self.verification_token = rand(999_999).to_s.ljust(6, "0")
     else