Add credentials using a generic EncryptedConfiguration class (#30067)

* WIP: Add credentials using a generic EncryptedConfiguration class

This is sketch code so far.

* Flesh out EncryptedConfiguration and test it

* Better name

* Add command and generator for credentials

* Use the Pathnames

* Extract EncryptedFile from EncryptedConfiguration and add serializers

* Test EncryptedFile

* Extract serializer validation

* Stress the point about losing comments

* Allow encrypted configuration to be read without parsing for display

* Use credentials by default and base them on the master key

* Derive secret_key_base in test/dev, source it from credentials in other envs

And document the usage.

* Document the new credentials setup

* Stop generating the secrets.yml file now that we have credentials

* Document what we should have instead

Still need to make it happen, tho.

* [ci skip] Keep wording to `key base`; prefer defaults.

Usually we say we change defaults, not "spec" out a release.

Can't use backticks in our sdoc generated documentation either.

* Abstract away OpenSSL; prefer MessageEncryptor.

* Spare needless new when raising.

* Encrypted file test shouldn't depend on subclass.

* [ci skip] Some woordings.

* Ditch serializer future coding.

* I said flip it. Flip it good.

* [ci skip] Move require_master_key to the real production.rb.

* Add require_master_key to abort the boot process.

In case the master key is required in a certain environment
we should inspect that the key is there and abort if it isn't.

* Print missing key message and exit immediately.

Spares us a lengthy backtrace and prevents further execution.

I've verified the behavior in a test app, but couldn't figure the
test out as loading the app just exits immediately with:

```
/Users/kasperhansen/Documents/code/rails/activesupport/lib/active_support/testing/isolation.rb:23:in `load': marshal data too short (ArgumentError)
	from /Users/kasperhansen/Documents/code/rails/activesupport/lib/active_support/testing/isolation.rb:23:in `run'
	from /Users/kasperhansen/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/minitest-5.10.2/lib/minitest.rb:830:in `run_one_method'
	from /Users/kasperhansen/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/minitest-5.10.2/lib/minitest/parallel.rb:32:in `block (2 levels) in start'
```

It's likely we need to capture and prevent the exit somehow.
Kernel.stub(:exit) didn't work. Leaving it for tomorrow.

* Fix require_master_key config test.

Loading the app would trigger the `exit 1` per require_master_key's
semantics, which then aborted the test.

Fork and wait for the child process to finish, then inspect the
exit status.

Also check we aborted because of a missing master key, so something
else didn't just abort the boot.

Much <3 to @tenderlove for the tip.

* Support reading/writing configs via methods.

* Skip needless deep symbolizing.

* Remove save; test config reader elsewhere.

* Move secret_key_base check to when we're reading it.

Otherwise we'll abort too soon since we don't assign the secret_key_base
to secrets anymore.

* Add missing string literal comments; require unneeded yaml require.

* ya ya ya, rubocop.

* Add master_key/credentials after bundle.

Then we can reuse the existing message on `rails new bc4`.

It'll look like:

```
Using web-console 3.5.1 from https://github.com/rails/web-console.git (at master@ce985eb)
Using rails 5.2.0.alpha from source at `/Users/kasperhansen/Documents/code/rails`
Using sass-rails 5.0.6
Bundle complete! 16 Gemfile dependencies, 72 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
Adding config/master.key to store the master encryption key: 97070158c44b4675b876373a6bc9d5a0

Save this in a password manager your team can access.

If you lose the key, no one, including you, can access anything encrypted with it.

      create  config/master.key
```

And that'll be executed even if `--skip-bundle` was passed.

* Ensure test app has secret_key_base.

* Assign secret_key_base to app or omit.

* Merge noise

* Split options for dynamic delegation into its own method and use deep symbols to make it work

* Update error to point to credentials instead

* Appease Rubocop

* Validate secret_key_base when reading it.

Instead of relying on the validation in key_generator move that into
secret_key_base itself.

* Fix generator and secrets test.

Manually add config.read_encrypted_secrets since it's not there by default
anymore.

Move mentions of config/secrets.yml to config/credentials.yml.enc.

* Remove files I have no idea how they got here.

* [ci skip] swap secrets for credentials.

* [ci skip] And now, changelogs are coming.

28 files changed, 678 insertions, 123 deletions

diff --git a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
index a12cb00d36..f594b6f491 100644
--- a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
+++ b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
@@ -33,12 +33,12 @@ module ActionDispatch
     #
     #   Rails.application.config.session_store :cookie_store, key: '_your_app_session'
     #
-    # Configure your secret key in <tt>config/secrets.yml</tt>:
+    # By default, your secret key base is derived from your application name in
+    # the test and development environments. In all other environments, it is stored
+    # encrypted in the <tt>config/credentials.yml.enc</tt> file.
     #
-    #   development:
-    #     secret_key_base: 'secret key'
-    #
-    # To generate a secret key for an existing application, run <tt>rails secret</tt>.
+    # If your application was not updated to Rails 5.2 defaults, the secret_key_base
+    # will be found in the old <tt>config/secrets.yml</tt> file.
     #
     # If you are upgrading an existing Rails 3 app, you should leave your
     # existing secret_token in place and simply add the new secret_key_base.
diff --git a/activestorage/lib/active_storage/engine.rb b/activestorage/lib/active_storage/engine.rb
index a5562b32d3..590a36a30a 100644
--- a/activestorage/lib/active_storage/engine.rb
+++ b/activestorage/lib/active_storage/engine.rb
@@ -29,9 +29,7 @@ module ActiveStorage
 
     initializer "active_storage.verifier" do
       config.after_initialize do |app|
-        if app.secrets.secret_key_base.present?
-          ActiveStorage.verifier = app.message_verifier("ActiveStorage")
-        end
+        ActiveStorage.verifier = app.message_verifier("ActiveStorage")
       end
     end
 
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index ac1043df78..f158d5357d 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,22 @@
+*   Add `config/credentials.yml.enc` to store production app secrets.
+
+    Allows saving any authentication credentials for third party services
+    directly in repo encrypted with `config/master.key` or `ENV["RAILS_MASTER_KEY"]`.
+
+    This will eventually replace `Rails.application.secrets` and the encrypted
+    secrets introduced in Rails 5.1.
+
+    *DHH*, *Kasper Timm Hansen*
+
+*   Add `ActiveSupport::EncryptedFile` and `ActiveSupport::EncryptedConfiguration`.
+
+    Allows for stashing encrypted files or configuration directly in repo by
+    encrypting it with a key.
+
+    Backs the new credentials setup above, but can also be used independently.
+
+    *DHH*, *Kasper Timm Hansen*
+
 *   `Module#delegate_missing_to` now raises `DelegationError` if target is nil,
     similar to `Module#delegate`.
 
diff --git a/activesupport/lib/active_support/encrypted_configuration.rb b/activesupport/lib/active_support/encrypted_configuration.rb
new file mode 100644
index 0000000000..b403048627
--- /dev/null
+++ b/activesupport/lib/active_support/encrypted_configuration.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require "yaml"
+require "active_support/encrypted_file"
+require "active_support/ordered_options"
+require "active_support/core_ext/object/inclusion"
+require "active_support/core_ext/module/delegation"
+
+module ActiveSupport
+  class EncryptedConfiguration < EncryptedFile
+    delegate :[], :fetch, to: :config
+    delegate_missing_to :options
+
+    def initialize(config_path:, key_path:, env_key:)
+      super content_path: config_path, key_path: key_path, env_key: env_key
+    end
+
+    # Allow a config to be started without a file present
+    def read
+      super
+    rescue ActiveSupport::EncryptedFile::MissingContentError
+      ""
+    end
+
+    def config
+      @config ||= deserialize(read).deep_symbolize_keys
+    end
+
+    private
+      def options
+        @options ||= ActiveSupport::InheritableOptions.new(config)
+      end
+
+      def serialize(config)
+        config.present? ? YAML.dump(config) : ""
+      end
+
+      def deserialize(config)
+        config.present? ? YAML.load(config) : {}
+      end
+  end
+end
diff --git a/activesupport/lib/active_support/encrypted_file.rb b/activesupport/lib/active_support/encrypted_file.rb
new file mode 100644
index 0000000000..1c4c1cb457
--- /dev/null
+++ b/activesupport/lib/active_support/encrypted_file.rb
@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+require "pathname"
+require "active_support/message_encryptor"
+require "active_support/core_ext/string/strip"
+require "active_support/core_ext/module/delegation"
+
+module ActiveSupport
+  class EncryptedFile
+    class MissingContentError < RuntimeError
+      def initialize(content_path)
+        super "Missing encrypted content file in #{content_path}."
+      end
+    end
+
+    class MissingKeyError < RuntimeError
+      def initialize(key_path:, env_key:)
+        super \
+          "Missing encryption key to decrypt file with. " +
+          "Ask your team for your master key and write it to #{key_path} or put it in the ENV['#{env_key}']."
+      end
+    end
+
+    CIPHER = "aes-128-gcm"
+
+    def self.generate_key
+      SecureRandom.hex(ActiveSupport::MessageEncryptor.key_len(CIPHER))
+    end
+
+
+    attr_reader :content_path, :key_path, :env_key
+
+    def initialize(content_path:, key_path:, env_key:)
+      @content_path, @key_path = Pathname.new(content_path), Pathname.new(key_path)
+      @env_key = env_key
+    end
+
+    def key
+      read_env_key || read_key_file || handle_missing_key
+    end
+
+    def read
+      if content_path.exist?
+        decrypt content_path.binread
+      else
+        raise MissingContentError, content_path
+      end
+    end
+
+    def write(contents)
+      IO.binwrite "#{content_path}.tmp", encrypt(contents)
+      FileUtils.mv "#{content_path}.tmp", content_path
+    end
+
+    def change(&block)
+      writing read, &block
+    end
+
+
+    private
+      def writing(contents)
+        tmp_file = "#{content_path.basename}.#{Process.pid}"
+        tmp_path = Pathname.new File.join(Dir.tmpdir, tmp_file)
+        tmp_path.binwrite contents
+
+        yield tmp_path
+
+        updated_contents = tmp_path.binread
+
+        write(updated_contents) if updated_contents != contents
+      ensure
+        FileUtils.rm(tmp_path) if tmp_path.exist?
+      end
+
+
+      def encrypt(contents)
+        encryptor.encrypt_and_sign contents
+      end
+
+      def decrypt(contents)
+        encryptor.decrypt_and_verify contents
+      end
+
+      def encryptor
+        @encryptor ||= ActiveSupport::MessageEncryptor.new([ key ].pack("H*"), cipher: CIPHER)
+      end
+
+
+      def read_env_key
+        ENV[env_key]
+      end
+
+      def read_key_file
+        key_path.binread.strip if key_path.exist?
+      end
+
+      def handle_missing_key
+        raise MissingKeyError, key_path: key_path, env_key: env_key
+      end
+  end
+end
diff --git a/activesupport/lib/active_support/railtie.rb b/activesupport/lib/active_support/railtie.rb
index 2efe391d01..fe132ca7c6 100644
--- a/activesupport/lib/active_support/railtie.rb
+++ b/activesupport/lib/active_support/railtie.rb
@@ -49,6 +49,17 @@ module ActiveSupport
       Date.beginning_of_week_default = beginning_of_week_default
     end
 
+    initializer "active_support.require_master_key" do |app|
+      if app.config.respond_to?(:require_master_key) && app.config.require_master_key
+        begin
+          app.credentials.key
+        rescue ActiveSupport::EncryptedFile::MissingKeyError => error
+          $stderr.puts error.message
+          exit 1
+        end
+      end
+    end
+
     initializer "active_support.set_configs" do |app|
       app.config.active_support.each do |k, v|
         k = "#{k}="
diff --git a/activesupport/test/encrypted_configuration_test.rb b/activesupport/test/encrypted_configuration_test.rb
new file mode 100644
index 0000000000..53ea9e393f
--- /dev/null
+++ b/activesupport/test/encrypted_configuration_test.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/encrypted_configuration"
+
+class EncryptedConfigurationTest < ActiveSupport::TestCase
+  setup do
+    @credentials_config_path = File.join(Dir.tmpdir, "credentials.yml.enc")
+
+    @credentials_key_path = File.join(Dir.tmpdir, "master.key")
+    File.write(@credentials_key_path, ActiveSupport::EncryptedConfiguration.generate_key)
+
+    @credentials = ActiveSupport::EncryptedConfiguration.new \
+      config_path: @credentials_config_path, key_path: @credentials_key_path, env_key: "RAILS_MASTER_KEY"
+  end
+
+  teardown do
+    FileUtils.rm_rf @credentials_config_path
+    FileUtils.rm_rf @credentials_key_path
+  end
+
+  test "reading configuration by env key" do
+    FileUtils.rm_rf @credentials_key_path
+
+    begin
+      ENV["RAILS_MASTER_KEY"] = ActiveSupport::EncryptedConfiguration.generate_key
+      @credentials.write({ something: { good: true, bad: false } }.to_yaml)
+
+      assert @credentials[:something][:good]
+      assert_not @credentials.dig(:something, :bad)
+      assert_nil @credentials.fetch(:nothing, nil)
+    ensure
+      ENV["RAILS_MASTER_KEY"] = nil
+    end
+  end
+
+  test "reading configuration by key file" do
+    @credentials.write({ something: { good: true } }.to_yaml)
+
+    assert @credentials.something[:good]
+  end
+
+  test "change configuration by key file" do
+    @credentials.write({ something: { good: true } }.to_yaml)
+    @credentials.change do |config_file|
+      config = YAML.load(config_file.read)
+      config_file.write config.merge(new: "things").to_yaml
+    end
+
+    assert @credentials.something[:good]
+    assert_equal "things", @credentials[:new]
+  end
+
+  test "raises key error when accessing config via bang method" do
+    assert_raise(KeyError) { @credentials.something! }
+  end
+
+  private
+    def new_credentials_configuration
+      ActiveSupport::EncryptedConfiguration.new \
+        config_path: @credentials_config_path,
+        key_path: @credentials_key_path,
+        env_key: "RAILS_MASTER_KEY"
+    end
+end
diff --git a/activesupport/test/encrypted_file_test.rb b/activesupport/test/encrypted_file_test.rb
new file mode 100644
index 0000000000..7259726d08
--- /dev/null
+++ b/activesupport/test/encrypted_file_test.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/encrypted_file"
+
+class EncryptedFileTest < ActiveSupport::TestCase
+  setup do
+    @content = "One little fox jumped over the hedge"
+
+    @content_path = File.join(Dir.tmpdir, "content.txt.enc")
+
+    @key_path = File.join(Dir.tmpdir, "content.txt.key")
+    File.write(@key_path, ActiveSupport::EncryptedFile.generate_key)
+
+    @encrypted_file = ActiveSupport::EncryptedFile.new \
+      content_path: @content_path, key_path: @key_path, env_key: "CONTENT_KEY"
+  end
+
+  teardown do
+    FileUtils.rm_rf @content_path
+    FileUtils.rm_rf @key_path
+  end
+
+  test "reading content by env key" do
+    FileUtils.rm_rf @key_path
+
+    begin
+      ENV["CONTENT_KEY"] = ActiveSupport::EncryptedFile.generate_key
+      @encrypted_file.write @content
+
+      assert_equal @content, @encrypted_file.read
+    ensure
+      ENV["CONTENT_KEY"] = nil
+    end
+  end
+
+  test "reading content by key file" do
+    @encrypted_file.write(@content)
+    assert_equal @content, @encrypted_file.read
+  end
+
+  test "change content by key file" do
+    @encrypted_file.write(@content)
+    @encrypted_file.change do |file|
+      file.write(file.read + " and went by the lake")
+    end
+
+    assert_equal "#{@content} and went by the lake", @encrypted_file.read
+  end
+end
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index e61adda7c3..5057059898 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Derive `secret_key_base` from the app name in development and test environments.
+
+    Spares away needless secret configs.
+
+    *DHH*, *Kasper Timm Hansen*
+
 *   Support multiple versions arguments for `gem` method of Generators.
 
     *Yoshiyuki Hirano*
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index 72f8bf0e14..6ce8b0b2d9 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -5,6 +5,7 @@ require "active_support/core_ext/hash/keys"
 require "active_support/core_ext/object/blank"
 require "active_support/key_generator"
 require "active_support/message_verifier"
+require "active_support/encrypted_configuration"
 require_relative "engine"
 require_relative "secrets"
 
@@ -171,12 +172,9 @@ module Rails
       # number of iterations selected based on consultation with the google security
       # team. Details at https://github.com/rails/rails/pull/6952#issuecomment-7661220
       @caching_key_generator ||=
-        if secrets.secret_key_base
-          unless secrets.secret_key_base.kind_of?(String)
-            raise ArgumentError, "`secret_key_base` for #{Rails.env} environment must be a type of String, change this value in `config/secrets.yml`"
-          end
-          key_generator = ActiveSupport::KeyGenerator.new(secrets.secret_key_base, iterations: 1000)
-          ActiveSupport::CachingKeyGenerator.new(key_generator)
+        if secret_key_base
+          ActiveSupport::CachingKeyGenerator.new \
+            ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
         else
           ActiveSupport::LegacyKeyGenerator.new(secrets.secret_token)
         end
@@ -246,13 +244,11 @@ module Rails
     # will be used by middlewares and engines to configure themselves.
     def env_config
       @app_env_config ||= begin
-        validate_secret_key_config!
-
         super.merge(
           "action_dispatch.parameter_filter" => config.filter_parameters,
           "action_dispatch.redirect_filter" => config.filter_redirect,
           "action_dispatch.secret_token" => secrets.secret_token,
-          "action_dispatch.secret_key_base" => secrets.secret_key_base,
+          "action_dispatch.secret_key_base" => secret_key_base,
           "action_dispatch.show_exceptions" => config.action_dispatch.show_exceptions,
           "action_dispatch.show_detailed_exceptions" => config.consider_all_requests_local,
           "action_dispatch.logger" => Rails.logger,
@@ -406,6 +402,33 @@ module Rails
       @secrets = secrets
     end
 
+    # The secret_key_base is used as the input secret to the application's key generator, which in turn
+    # is used to create all the MessageVerfiers, including the one that signs and encrypts cookies.
+    #
+    # In test and development, this is simply derived as a MD5 hash of the application's name.
+    #
+    # In all other environments, we look for it first in ENV["SECRET_KEY_BASE"],
+    # then credentials[:secret_key_base], and finally secrets.secret_key_base. For most applications,
+    # the correct place to store it is in the encrypted credentials file.
+    def secret_key_base
+      if Rails.env.test? || Rails.env.development?
+        Digest::MD5.hexdigest self.class.name
+      else
+        validate_secret_key_base \
+          ENV["SECRET_KEY_BASE"] || credentials.secret_key_base || secrets.secret_key_base
+      end
+    end
+
+    # Decrypts the credentials hash as kept in `config/credentials.yml.enc`. This file is encrypted with
+    # the Rails master key, which is either taken from ENV["RAILS_MASTER_KEY"] or from loading
+    # `config/master.key`.
+    def credentials
+      @credentials ||= ActiveSupport::EncryptedConfiguration.new \
+        config_path: Rails.root.join("config/credentials.yml.enc"),
+        key_path: Rails.root.join("config/master.key"),
+        env_key: "RAILS_MASTER_KEY"
+    end
+
     def to_app #:nodoc:
       self
     end
@@ -504,14 +527,13 @@ module Rails
       default_stack.build_stack
     end
 
-    def validate_secret_key_config! #:nodoc:
-      if secrets.secret_key_base.blank?
-        ActiveSupport::Deprecation.warn "You didn't set `secret_key_base`. " \
-          "Read the upgrade documentation to learn more about this new config option."
-
-        if secrets.secret_token.blank?
-          raise "Missing `secret_key_base` for '#{Rails.env}' environment, set this value in `config/secrets.yml`"
-        end
+    def validate_secret_key_base(secret_key_base)
+      if secret_key_base.is_a?(String) && secret_key_base.present?
+        secret_key_base
+      elsif secret_key_base
+        raise ArgumentError, "`secret_key_base` for #{Rails.env} environment must be a type of String`"
+      elsif secrets.secret_token.blank?
+        raise ArgumentError, "Missing `secret_key_base` for '#{Rails.env}' environment, set this string with `rails credentials:edit`"
       end
     end
 
diff --git a/railties/lib/rails/commands/credentials/USAGE b/railties/lib/rails/commands/credentials/USAGE
new file mode 100644
index 0000000000..5bd9f940fd
--- /dev/null
+++ b/railties/lib/rails/commands/credentials/USAGE
@@ -0,0 +1,40 @@
+=== Storing Encrypted Credentials in Source Control
+
+The Rails `credentials` commands provide access to encrypted credentials,
+so you can safely store access tokens, database passwords, and the like
+safely inside the app without relying on a mess of ENVs.
+
+This also allows for atomic deploys: no need to coordinate key changes
+to get everything working as the keys are shipped with the code.
+
+=== Setup
+
+Applications after Rails 5.2 automatically have a basic credentials file generated
+that just contains the secret_key_base used by the MessageVerifiers, like the one
+signing and encrypting cookies.
+
+For applications created prior to Rails 5.2, we'll automatically generate a new
+credentials file in `config/credentials.yml.enc` the first time you run `bin/rails credentials:edit`.
+If you didn't have a master key saved in `config/master.key`, that'll be created too.
+
+Don't lose this master key! Put it in a password manager your team can access.
+Should you lose it no one, including you, will be able to access any encrypted
+credentials.
+
+Don't commit the key! Add `config/master.key` to your source control's
+ignore file. If you use Git, Rails handles this for you.
+
+Rails also looks for the master key in `ENV["RAILS_MASTER_KEY"]`, if that's easier to manage.
+
+You could prepend that to your server's start command like this:
+
+   RAILS_MASTER_KEY="very-secret-and-secure" server.start
+
+=== Editing Credentials
+
+This will open a temporary file in `$EDITOR` with the decrypted contents to edit
+the encrypted credentials.
+
+When the temporary file is next saved the contents are encrypted and written to
+`config/credentials.yml.enc` while the file itself is destroyed to prevent credentials
+from leaking.
diff --git a/railties/lib/rails/commands/credentials/credentials_command.rb b/railties/lib/rails/commands/credentials/credentials_command.rb
new file mode 100644
index 0000000000..39a4e3c833
--- /dev/null
+++ b/railties/lib/rails/commands/credentials/credentials_command.rb
@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+require "active_support"
+
+module Rails
+  module Command
+    class CredentialsCommand < Rails::Command::Base # :nodoc:
+      no_commands do
+        def help
+          say "Usage:\n  #{self.class.banner}"
+          say ""
+          say self.class.desc
+        end
+      end
+
+      def edit
+        require_application_and_environment!
+
+        ensure_editor_available || (return)
+        ensure_master_key_has_been_added
+        ensure_credentials_have_been_added
+
+        change_credentials_in_system_editor
+
+        say "New credentials encrypted and saved."
+      rescue Interrupt
+        say "Aborted changing credentials: nothing saved."
+      rescue ActiveSupport::EncryptedFile::MissingKeyError => error
+        say error.message
+      end
+
+      def show
+        require_application_and_environment!
+        say Rails.application.credentials.read.presence ||
+          "No credentials have been added yet. Use bin/rails credentials:edit to change that."
+      end
+
+      private
+        def ensure_editor_available
+          if ENV["EDITOR"].to_s.empty?
+            say "No $EDITOR to open credentials in. Assign one like this:"
+            say ""
+            say %(EDITOR="mate --wait" bin/rails credentials:edit)
+            say ""
+            say "For editors that fork and exit immediately, it's important to pass a wait flag,"
+            say "otherwise the credentials will be saved immediately with no chance to edit."
+
+            false
+          else
+            true
+          end
+        end
+
+        def ensure_master_key_has_been_added
+          master_key_generator.add_master_key_file
+          master_key_generator.ignore_master_key_file
+        end
+
+        def ensure_credentials_have_been_added
+          credentials_generator.add_credentials_file_silently
+        end
+
+        def change_credentials_in_system_editor
+          Rails.application.credentials.change do |tmp_path|
+            system("#{ENV["EDITOR"]} #{tmp_path}")
+          end
+        end
+
+
+        def master_key_generator
+          require_relative "../../generators"
+          require_relative "../../generators/rails/master_key/master_key_generator"
+
+          Rails::Generators::MasterKeyGenerator.new
+        end
+
+        def credentials_generator
+          require_relative "../../generators"
+          require_relative "../../generators/rails/credentials/credentials_generator"
+
+          Rails::Generators::CredentialsGenerator.new
+        end
+    end
+  end
+end
diff --git a/railties/lib/rails/generators/rails/app/app_generator.rb b/railties/lib/rails/generators/rails/app/app_generator.rb
index 0f73cc4755..c67baa5e91 100644
--- a/railties/lib/rails/generators/rails/app/app_generator.rb
+++ b/railties/lib/rails/generators/rails/app/app_generator.rb
@@ -111,7 +111,6 @@ module Rails
         template "routes.rb"
         template "application.rb"
         template "environment.rb"
-        template "secrets.yml"
         template "cable.yml" unless options[:skip_action_cable]
         template "puma.rb"   unless options[:skip_puma]
         template "spring.rb" if spring_install?
@@ -159,6 +158,22 @@ module Rails
       end
     end
 
+    def master_key
+      require_relative "../master_key/master_key_generator"
+
+      after_bundle do
+        Rails::Generators::MasterKeyGenerator.new.add_master_key_file
+      end
+    end
+
+    def credentials
+      require_relative "../credentials/credentials_generator"
+
+      after_bundle do
+        Rails::Generators::CredentialsGenerator.new.add_credentials_file_silently
+      end
+    end
+
     def database_yml
       template "config/databases/#{options[:database]}.yml", "config/database.yml"
     end
@@ -289,6 +304,14 @@ module Rails
       end
       remove_task :update_config_files
 
+      def create_master_key
+        build(:master_key)
+      end
+
+      def create_credentials
+        build(:credentials)
+      end
+
       def display_upgrade_guide_info
         say "\nAfter this, check Rails upgrade guide at http://guides.rubyonrails.org/upgrading_ruby_on_rails.html for more details about upgrading your app."
       end
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
index f68e13aa8b..2e0b555f6f 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
@@ -14,10 +14,9 @@ Rails.application.configure do
   config.consider_all_requests_local       = false
   config.action_controller.perform_caching = true
 
-  # Attempt to read encrypted secrets from `config/secrets.yml.enc`.
-  # Requires an encryption key in `ENV["RAILS_MASTER_KEY"]` or
-  # `config/secrets.yml.key`.
-  config.read_encrypted_secrets = true
+  # Ensures that a master key has been made available in either ENV["RAILS_MASTER_KEY"]
+  # or in config/master.key. This key is used to decrypt credentials (and other encrypted files).
+  # config.require_master_key = true
 
   # Disable serving static files from the `/public` folder by default since
   # Apache or NGINX already handles this.
diff --git a/railties/lib/rails/generators/rails/app/templates/gitignore b/railties/lib/rails/generators/rails/app/templates/gitignore
index 83a7b211aa..c37f01a848 100644
--- a/railties/lib/rails/generators/rails/app/templates/gitignore
+++ b/railties/lib/rails/generators/rails/app/templates/gitignore
@@ -7,6 +7,9 @@
 # Ignore bundler config.
 /.bundle
 
+# Ignore master key for decrypting credentials and more.
+/config/master.key
+
 <% if sqlite3? -%>
 # Ignore the default SQLite database.
 /db/*.sqlite3
diff --git a/railties/lib/rails/generators/rails/credentials/credentials_generator.rb b/railties/lib/rails/generators/rails/credentials/credentials_generator.rb
new file mode 100644
index 0000000000..ddcccd5ce5
--- /dev/null
+++ b/railties/lib/rails/generators/rails/credentials/credentials_generator.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require_relative "../../base"
+require_relative "../master_key/master_key_generator"
+require "active_support/encrypted_configuration"
+
+module Rails
+  module Generators
+    class CredentialsGenerator < Base
+      CONFIG_PATH = "config/credentials.yml.enc"
+      KEY_PATH    = "config/master.key"
+
+      def add_credentials_file
+        unless File.exist?(CONFIG_PATH)
+          template = credentials_template
+
+          say "Adding #{CONFIG_PATH} to store encrypted credentials."
+          say ""
+          say "The following content has been encrypted with the Rails master key:"
+          say ""
+          say template, :on_green
+          say ""
+
+          add_credentials_file_silently(template)
+
+          say "You can edit encrypted credentials with `bin/rails credentials:edit`."
+          say ""
+        end
+      end
+
+      def add_credentials_file_silently(template = nil)
+        unless File.exist?(CONFIG_PATH)
+          setup = { config_path: CONFIG_PATH, key_path: KEY_PATH, env_key: "RAILS_MASTER_KEY" }
+          ActiveSupport::EncryptedConfiguration.new(setup).write(credentials_template)
+        end
+      end
+
+      private
+        def credentials_template
+          "# amazon:\n#  access_key_id: 123\n#  secret_access_key: 345\n\n" +
+          "# Used as the base secret for all MessageVerifiers in Rails, including the one protecting cookies.\n" +
+          "secret_key_base: #{SecureRandom.hex(64)}"
+        end
+    end
+  end
+end
diff --git a/railties/lib/rails/generators/rails/master_key/master_key_generator.rb b/railties/lib/rails/generators/rails/master_key/master_key_generator.rb
new file mode 100644
index 0000000000..36a0b69e76
--- /dev/null
+++ b/railties/lib/rails/generators/rails/master_key/master_key_generator.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require_relative "../../base"
+require "pathname"
+require "active_support/encrypted_file"
+
+module Rails
+  module Generators
+    class MasterKeyGenerator < Base
+      MASTER_KEY_PATH = Pathname.new("config/master.key")
+
+      def add_master_key_file
+        unless MASTER_KEY_PATH.exist?
+          key = ActiveSupport::EncryptedFile.generate_key
+
+          say "Adding #{MASTER_KEY_PATH} to store the master encryption key: #{key}"
+          say ""
+          say "Save this in a password manager your team can access."
+          say ""
+          say "If you lose the key, no one, including you, can access anything encrypted with it."
+
+          say ""
+          add_master_key_file_silently key
+          say ""
+        end
+      end
+
+      def add_master_key_file_silently(key = nil)
+        create_file MASTER_KEY_PATH, key || ActiveSupport::EncryptedFile.generate_key
+      end
+
+      def ignore_master_key_file
+        if File.exist?(".gitignore")
+          unless File.read(".gitignore").include?(key_ignore)
+            say "Ignoring #{MASTER_KEY_PATH} so it won't end up in Git history:"
+            say ""
+            append_to_file ".gitignore", key_ignore
+            say ""
+          end
+        else
+          say "IMPORTANT: Don't commit #{MASTER_KEY_PATH}. Add this to your ignore file:"
+          say key_ignore, :on_green
+          say ""
+        end
+      end
+
+      private
+        def key_ignore
+          [ "", "# Ignore master key for decrypting credentials and more.", MASTER_KEY_PATH, "" ].join("\n")
+        end
+    end
+  end
+end
diff --git a/railties/test/abstract_unit.rb b/railties/test/abstract_unit.rb
index a63b7a8377..b42f37d6b9 100644
--- a/railties/test/abstract_unit.rb
+++ b/railties/test/abstract_unit.rb
@@ -15,7 +15,6 @@ require "rails/all"
 module TestApp
   class Application < Rails::Application
     config.root = __dir__
-    secrets.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
   end
 end
 
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 64939e4ab4..c1a80eaeaf 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -476,45 +476,35 @@ module ApplicationTests
 
     test "application message verifier can be used when the key_generator is ActiveSupport::LegacyKeyGenerator" do
       app_file "config/initializers/secret_token.rb", <<-RUBY
+        Rails.application.credentials.secret_key_base = nil
         Rails.application.config.secret_token = "b3c631c314c0bbca50c1b2843150fe33"
       RUBY
-      app_file "config/secrets.yml", <<-YAML
-        development:
-          secret_key_base:
-      YAML
 
-      app "development"
+      app "production"
 
-      assert_equal app.env_config["action_dispatch.key_generator"], Rails.application.key_generator
-      assert_equal app.env_config["action_dispatch.key_generator"].class, ActiveSupport::LegacyKeyGenerator
+      assert_kind_of ActiveSupport::LegacyKeyGenerator, Rails.application.key_generator
       message = app.message_verifier(:sensitive_value).generate("some_value")
       assert_equal "some_value", Rails.application.message_verifier(:sensitive_value).verify(message)
     end
 
-    test "warns when secrets.secret_key_base is blank and config.secret_token is set" do
+    test "raises when secret_key_base is blank" do
       app_file "config/initializers/secret_token.rb", <<-RUBY
-        Rails.application.config.secret_token = "b3c631c314c0bbca50c1b2843150fe33"
+        Rails.application.credentials.secret_key_base = nil
       RUBY
-      app_file "config/secrets.yml", <<-YAML
-        development:
-          secret_key_base:
-      YAML
-
-      app "development"
 
-      assert_deprecated(/You didn't set `secret_key_base`./) do
-        app.env_config
+      error = assert_raise(ArgumentError) do
+        app "production"
       end
+      assert_match(/Missing `secret_key_base`./, error.message)
     end
 
-    test "raise when secrets.secret_key_base is not a type of string" do
-      app_file "config/secrets.yml", <<-YAML
-        development:
-          secret_key_base: 123
-      YAML
+    test "raise when secret_key_base is not a type of string" do
+      add_to_config <<-RUBY
+        Rails.application.credentials.secret_key_base = 123
+      RUBY
 
       assert_raise(ArgumentError) do
-        app "development"
+        app "production"
       end
     end
 
@@ -534,7 +524,7 @@ module ApplicationTests
 
     test "application verifier can build different verifiers" do
       make_basic_app do |application|
-        application.secrets.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
+        application.credentials.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
         application.config.session_store :disabled
       end
 
@@ -652,37 +642,15 @@ module ApplicationTests
 
     test "uses ActiveSupport::LegacyKeyGenerator as app.key_generator when secrets.secret_key_base is blank" do
       app_file "config/initializers/secret_token.rb", <<-RUBY
+        Rails.application.credentials.secret_key_base = nil
         Rails.application.config.secret_token = "b3c631c314c0bbca50c1b2843150fe33"
       RUBY
-      app_file "config/secrets.yml", <<-YAML
-        development:
-          secret_key_base:
-      YAML
 
-      app "development"
+      app "production"
 
       assert_equal "b3c631c314c0bbca50c1b2843150fe33", app.config.secret_token
-      assert_nil app.secrets.secret_key_base
-      assert_equal app.key_generator.class, ActiveSupport::LegacyKeyGenerator
-    end
-
-    test "uses ActiveSupport::LegacyKeyGenerator with config.secret_token as app.key_generator when secrets.secret_key_base is blank" do
-      app_file "config/initializers/secret_token.rb", <<-RUBY
-        Rails.application.config.secret_token = ""
-      RUBY
-      app_file "config/secrets.yml", <<-YAML
-        development:
-          secret_key_base:
-      YAML
-
-      app "development"
-
-      assert_equal "", app.config.secret_token
-      assert_nil app.secrets.secret_key_base
-      e = assert_raise ArgumentError do
-        app.key_generator
-      end
-      assert_match(/\AA secret is required/, e.message)
+      assert_nil app.credentials.secret_key_base
+      assert_kind_of ActiveSupport::LegacyKeyGenerator, app.key_generator
     end
 
     test "that nested keys are symbolized the same as parents for hashes more than one level deep" do
@@ -699,6 +667,20 @@ module ApplicationTests
       assert_equal "697361616320736c6f616e2028656c6f7265737429", app.secrets.smtp_settings[:password]
     end
 
+    test "require_master_key aborts app boot when missing key" do
+      skip "can't run without fork" unless Process.respond_to?(:fork)
+
+      remove_file "config/master.key"
+      add_to_config "config.require_master_key = true"
+
+      error = capture(:stderr) do
+        Process.wait(Process.fork { app "development" })
+      end
+
+      assert_equal 1, $?.exitstatus
+      assert_match(/Missing.*RAILS_MASTER_KEY/, error)
+    end
+
     test "protect from forgery is the default in a new app" do
       make_basic_app
 
diff --git a/railties/test/application/middleware/sendfile_test.rb b/railties/test/application/middleware/sendfile_test.rb
index 4731396029..9def3a0ce7 100644
--- a/railties/test/application/middleware/sendfile_test.rb
+++ b/railties/test/application/middleware/sendfile_test.rb
@@ -15,10 +15,6 @@ module ApplicationTests
       teardown_app
     end
 
-    def app
-      @app ||= Rails.application
-    end
-
     define_method :simple_controller do
       class ::OmgController < ActionController::Base
         def index
diff --git a/railties/test/application/middleware/session_test.rb b/railties/test/application/middleware/session_test.rb
index 15acfe93e9..a17988235a 100644
--- a/railties/test/application/middleware/session_test.rb
+++ b/railties/test/application/middleware/session_test.rb
@@ -337,31 +337,37 @@ module ApplicationTests
 
       add_to_config <<-RUBY
         # Use a static key
-        secrets.secret_key_base = "known key base"
+        Rails.application.credentials.secret_key_base = "known key base"
 
         # Enable AEAD cookies
         config.action_dispatch.use_authenticated_cookie_encryption = true
       RUBY
 
-      require "#{app_path}/config/environment"
+      begin
+        old_rails_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "production"
 
-      get "/foo/write_raw_session"
-      get "/foo/read_session"
-      assert_equal "1", last_response.body
+        require "#{app_path}/config/environment"
 
-      get "/foo/write_session"
-      get "/foo/read_session"
-      assert_equal "2", last_response.body
+        get "/foo/write_raw_session"
+        get "/foo/read_session"
+        assert_equal "1", last_response.body
 
-      get "/foo/read_encrypted_cookie"
-      assert_equal "2", last_response.body
+        get "/foo/write_session"
+        get "/foo/read_session"
+        assert_equal "2", last_response.body
 
-      cipher = "aes-256-gcm"
-      secret = app.key_generator.generate_key("authenticated encrypted cookie")
-      encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
+        get "/foo/read_encrypted_cookie"
+        assert_equal "2", last_response.body
 
-      get "/foo/read_raw_cookie"
-      assert_equal 2, encryptor.decrypt_and_verify(last_response.body)["foo"]
+        cipher = "aes-256-gcm"
+        secret = app.key_generator.generate_key("authenticated encrypted cookie")
+        encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
+
+        get "/foo/read_raw_cookie"
+        assert_equal 2, encryptor.decrypt_and_verify(last_response.body)["foo"]
+      ensure
+        ENV["RAILS_ENV"] = old_rails_env
+      end
     end
 
     test "session upgrading legacy signed cookies to new signed cookies" do
@@ -400,26 +406,32 @@ module ApplicationTests
 
       add_to_config <<-RUBY
         secrets.secret_token = "3b7cd727ee24e8444053437c36cc66c4"
-        secrets.secret_key_base = nil
+        Rails.application.credentials.secret_key_base = nil
       RUBY
 
-      require "#{app_path}/config/environment"
+      begin
+        old_rails_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "production"
 
-      get "/foo/write_raw_session"
-      get "/foo/read_session"
-      assert_equal "1", last_response.body
+        require "#{app_path}/config/environment"
 
-      get "/foo/write_session"
-      get "/foo/read_session"
-      assert_equal "2", last_response.body
+        get "/foo/write_raw_session"
+        get "/foo/read_session"
+        assert_equal "1", last_response.body
 
-      get "/foo/read_signed_cookie"
-      assert_equal "2", last_response.body
+        get "/foo/write_session"
+        get "/foo/read_session"
+        assert_equal "2", last_response.body
 
-      verifier = ActiveSupport::MessageVerifier.new(app.secrets.secret_token)
+        get "/foo/read_signed_cookie"
+        assert_equal "2", last_response.body
 
-      get "/foo/read_raw_cookie"
-      assert_equal 2, verifier.verify(last_response.body)["foo"]
+        verifier = ActiveSupport::MessageVerifier.new(app.secrets.secret_token)
+
+        get "/foo/read_raw_cookie"
+        assert_equal 2, verifier.verify(last_response.body)["foo"]
+      ensure
+        ENV["RAILS_ENV"] = old_rails_env
+      end
     end
 
     test "calling reset_session on request does not trigger an error for API apps" do
diff --git a/railties/test/application/url_generation_test.rb b/railties/test/application/url_generation_test.rb
index 4f962db6c4..f22b9fda3d 100644
--- a/railties/test/application/url_generation_test.rb
+++ b/railties/test/application/url_generation_test.rb
@@ -16,7 +16,6 @@ module ApplicationTests
       require "action_view/railtie"
 
       class MyApp < Rails::Application
-        secrets.secret_key_base = "3b7cd727ee24e8444053437c36cc66c4"
         config.session_store :cookie_store, key: "_myapp_session"
         config.active_support.deprecation = :log
         config.eager_load = false
diff --git a/railties/test/generators/api_app_generator_test.rb b/railties/test/generators/api_app_generator_test.rb
index d141b1d4b4..7791d472d8 100644
--- a/railties/test/generators/api_app_generator_test.rb
+++ b/railties/test/generators/api_app_generator_test.rb
@@ -125,7 +125,7 @@ class ApiAppGeneratorTest < Rails::Generators::TestCase
         config/locales/en.yml
         config/puma.rb
         config/routes.rb
-        config/secrets.yml
+        config/credentials.yml.enc
         config/spring.rb
         config/storage.yml
         db
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index f64ebf5f1f..904e2a5c84 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -64,7 +64,7 @@ DEFAULT_APP_FILES = %w(
   config/locales/en.yml
   config/puma.rb
   config/routes.rb
-  config/secrets.yml
+  config/credentials.yml.enc
   config/spring.rb
   config/storage.yml
   db
@@ -287,8 +287,6 @@ class AppGeneratorTest < Rails::Generators::TestCase
     run_generator [app_root, "--skip-action-cable"]
 
     FileUtils.cd(app_root) do
-      # For avoid conflict file
-      FileUtils.rm("#{app_root}/config/secrets.yml")
       quietly { system("bin/rails app:update") }
     end
 
diff --git a/railties/test/generators/shared_generator_tests.rb b/railties/test/generators/shared_generator_tests.rb
index 56c9b37e1b..654d16de65 100644
--- a/railties/test/generators/shared_generator_tests.rb
+++ b/railties/test/generators/shared_generator_tests.rb
@@ -149,7 +149,7 @@ module SharedGeneratorTests
     end
     assert_file "#{application_path}/config/environments/production.rb" do |content|
       assert_match(/# config\.action_mailer\.raise_delivery_errors = false/, content)
-      assert_match(/^  config\.read_encrypted_secrets = true/, content)
+      assert_match(/^  # config\.require_master_key = true/, content)
     end
   end
 
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index b590dac4fb..b7f214cb73 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -105,7 +105,6 @@ module TestHelpers
     def build_app(options = {})
       @prev_rails_env = ENV["RAILS_ENV"]
       ENV["RAILS_ENV"] = "development"
-      ENV["SECRET_KEY_BASE"] ||= SecureRandom.hex(16)
 
       FileUtils.rm_rf(app_path)
       FileUtils.cp_r(app_template_path, app_path)
@@ -163,9 +162,10 @@ module TestHelpers
       require "action_controller/railtie"
       require "action_view/railtie"
 
-      @app = Class.new(Rails::Application)
+      @app = Class.new(Rails::Application) do
+        def self.name; "RailtiesTestApp"; end
+      end
       @app.config.eager_load = false
-      @app.secrets.secret_key_base = "3b7cd727ee24e8444053437c36cc66c4"
       @app.config.session_store :cookie_store, key: "_myapp_session"
       @app.config.active_support.deprecation = :log
       @app.config.active_support.test_order = :random
diff --git a/railties/test/path_generation_test.rb b/railties/test/path_generation_test.rb
index d4dfa8e4a6..849b183b37 100644
--- a/railties/test/path_generation_test.rb
+++ b/railties/test/path_generation_test.rb
@@ -58,12 +58,14 @@ class PathGenerationTest < ActiveSupport::TestCase
     Rails.logger    = Logger.new nil
 
     app = Class.new(Rails::Application) {
+      def self.name; "ScriptNameTestApp"; end
+
       attr_accessor :controller
+
       def initialize
         super
         app = self
         @routes = TestSet.new ->(c) { app.controller = c }
-        secrets.secret_key_base = "foo"
         secrets.secret_token = "foo"
       end
       def app; routes; end
diff --git a/railties/test/secrets_test.rb b/railties/test/secrets_test.rb
index a394f5661e..888fee173a 100644
--- a/railties/test/secrets_test.rb
+++ b/railties/test/secrets_test.rb
@@ -176,6 +176,10 @@ class Rails::SecretsTest < ActiveSupport::TestCase
           Rails::Generators::EncryptedSecretsGenerator.start
         end
 
+        add_to_config <<-RUBY
+          config.read_encrypted_secrets = true
+        RUBY
+
         yield
       end
     end