FEATURE: Hash user API keys in the database (#9344)

The 'key' column will be dropped in a future commit.

db/migrate/20200403100259_add_key_hash_to_user_api_key.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class AddKeyHashToUserApiKey < ActiveRecord::Migration[6.0]
+  def up
+    add_column :user_api_keys, :key_hash, :string
+
+    batch_size = 500
+    loop do
+      rows = DB
+        .query("SELECT id, key FROM user_api_keys WHERE key_hash IS NULL LIMIT #{batch_size}")
+        .map { |row| { id: row.id, key_hash: Digest::SHA256.hexdigest(key) } }
+
+      break if rows.size == 0
+
+      data_string = rows.map { |r| "(#{r[:id]}, '#{r[:key_hash]}')" }.join(",")
+      execute <<~SQL
+        UPDATE user_api_keys
+        SET key_hash = data.key_hash
+        FROM (VALUES #{data_string}) AS data(id, key_hash)
+        WHERE user_api_keys.id = data.id
+      SQL
+
+      break if rows.size < batch_size
+    end
+
+    change_column_null :user_api_keys, :key_hash, false
+  end
+
+  def down
+    drop_column :user_api_keys, :key_hash, :string
+  end
+end