DEV: Hash tokens stored from email_tokens (#14493)

This commit adds token_hash and scopes columns to email_tokens table.
token_hash is a replacement for the token column to avoid storing email
tokens in plaintext as it can pose a security risk. The new scope column
ensures that email tokens cannot be used to perform a different action
than the one intended.

To sum up, this commit:

* Adds token_hash and scope to email_tokens

* Reuses code that schedules critical_user_email

* Refactors EmailToken.confirm and EmailToken.atomic_confirm methods

* Periodically cleans old, unconfirmed or expired email tokens

db/migrate/20210929215543_add_token_hash_to_email_token.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class AddTokenHashToEmailToken < ActiveRecord::Migration[6.1]
+  def up
+    add_column :email_tokens, :token_hash, :string
+
+    loop do
+      rows = DB
+        .query("SELECT id, token FROM email_tokens WHERE token_hash IS NULL LIMIT 500")
+        .map { |row| { id: row.id, token_hash: Digest::SHA256.hexdigest(row.token) } }
+
+      break if rows.size == 0
+
+      data_string = rows.map { |r| "(#{r[:id]}, '#{r[:token_hash]}')" }.join(",")
+      execute <<~SQL
+        UPDATE email_tokens
+        SET token_hash = data.token_hash
+        FROM (VALUES #{data_string}) AS data(id, token_hash)
+        WHERE email_tokens.id = data.id
+      SQL
+    end
+
+    change_column_null :email_tokens, :token_hash, false
+  end
+
+  def down
+    drop_column :email_tokens, :token_hash, :string
+  end
+end

db/migrate/20211005163152_add_scope_to_email_token.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class AddScopeToEmailToken < ActiveRecord::Migration[6.1]
+  def up
+    add_column :email_tokens, :scope, :integer
+  end
+
+  def down
+    drop_column :email_tokens, :scope, :integer
+  end
+end