Adds spam/CAPTCHA dev docs for REST API

- Also cleans up and fixes Vale warnings in other
  areas of spam/CAPTCHA docs

doc/.vale/gitlab/spelling-exceptions.txt

@@ -594,6 +594,7 @@ Sobelow
 Solargraph
 Solarized
 Sourcegraph
+spammable
 sparkline
 sparklines
 spidering

doc/development/spam_protection_and_captcha/graphql_api.md

@@ -13,28 +13,27 @@ related to changing a model's confidential/public flag.
 
 ## Add support to the GraphQL mutations
 
-This implementation is very similar to the controller implementation. You create a `spam_params`
-instance based on the request, and pass it to the relevant Service class constructor.
+The main steps are:
 
-The three main differences from the controller implementation are:
+1. Use `include Mutations::SpamProtection` in your mutation.
+1. Create a `spam_params` instance based on the request. Obtain the request from the context
+   via `context[:request]` when creating the `SpamParams` instance.
+1. Pass `spam_params` to the relevant Service class constructor.
+1. After you create or update the `Spammable` model instance, call `#check_spam_action_response!`
+   and pass it the model instance. This call:
+   1. Performs the necessary spam checks on the model.
+   1. If spam is detected:
+      - Raises a `GraphQL::ExecutionError` exception.
+      - Includes the relevant information added as error fields to the response via the `extensions:` parameter.
+        For more details on these fields, refer to the section in the GraphQL API documentation on
+        [Resolve mutations detected as spam](../../api/graphql/index.md#resolve-mutations-detected-as-spam).
 
-1. Use `include Mutations::SpamProtection` instead of `...JsonFormatActionsSupport`.
-1. Obtain the request from the context via `context[:request]` when creating the `SpamParams`
-   instance.
-1. After you create or updated the `Spammable` model instance, call `#check_spam_action_response!`
-   and pass it the model instance. This call will:
-    1. Perform the necessary spam checks on the model.
-    1. If spam is detected:
-       - Raise a `GraphQL::ExecutionError` exception.
-       - Include the relevant information added as error fields to the response via the `extensions:` parameter.
-       For more details on these fields, refer to the section on
-       [Spam and CAPTCHA support in the GraphQL API](../../api/graphql/index.md#resolve-mutations-detected-as-spam).
-
-       NOTE:
-       If you use the standard ApolloLink or Axios interceptor CAPTCHA support described
-       above, the field details are unimportant. They become important if you
-       attempt to use the GraphQL API directly to process a failed check for potential spam, and
-       resubmit the request with a solved CAPTCHA response.
+   NOTE:
+   If you use the standard ApolloLink or Axios interceptor CAPTCHA support described
+   above, you can ignore the field details, because they are handled
+   automatically. They become relevant if you attempt to use the GraphQL API directly to
+   process a failed check for potential spam, and resubmit the request with a solved
+   CAPTCHA response.
 
 For example:
 
@@ -57,10 +56,13 @@ module Mutations
         widget = service_response.payload[:widget]
         check_spam_action_response!(widget)
 
-        # If possible spam wasdetected, an exception would have been thrown by
+        # If possible spam was detected, an exception would have been thrown by
         # `#check_spam_action_response!`, so the normal resolve return logic can follow below.
       end
     end
   end
 end
 ```
+
+Refer to the [Exploratory Testing](exploratory_testing.md) section for instructions on how to test
+CAPTCHA behavior in the GraphQL API.

doc/development/spam_protection_and_captcha/index.md

@@ -16,7 +16,7 @@ To add this support, you must implement the following areas as applicable:
 1. [Model and Services](model_and_services.md): The basic prerequisite
    changes to the backend code which are required to add spam or CAPTCHA API and UI support
    for a feature which does not yet have support.
-1. REST API (Supported, documentation coming soon): The changes needed to add
+1. [REST API](rest_api.md): The changes needed to add
    spam or CAPTCHA support to Grape REST API endpoints. Refer to the related
    [REST API documentation](../../api/index.md#resolve-requests-detected-as-spam).
 1. [GraphQL API](graphql_api.md): The changes needed to add spam or CAPTCHA support to GraphQL

doc/development/spam_protection_and_captcha/rest_api.md

+---
+stage: Manage
+group: Authentication and Authorization
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# REST API spam protection and CAPTCHA support
+
+If the model can be modified via the REST API, you must also add support to all of the
+relevant API endpoints which may modify spammable or spam-related attributes. This
+definitely includes the `POST` and `PUT` mutations, but may also include others, such as those
+related to changing a model's confidential/public flag.
+
+## Add support to the REST endpoints
+
+The main steps are:
+
+1. Add `helpers SpammableActions::CaptchaCheck::RestApiActionsSupport` in your `resource`.
+1. Create a `spam_params` instance based on the request.
+1. Pass `spam_params` to the relevant Service class constructor.
+1. After you create or update the `Spammable` model instance, call `#check_spam_action_response!`,
+   save the created or updated instance in a variable.
+1. Identify the error handling logic for the `failure` case of the request,
+   when create or update was not successful. These indicate possible spam detection,
+   which adds an error to the `Spammable` instance.
+   The error is usually similar to `render_api_error!` or `render_validation_error!`.
+1. Wrap the existing error handling logic in a
+   `with_captcha_check_rest_api(spammable: my_spammable_instance)` call, passing the `Spammable`
+   model instance you saved in a variable as the `spammable:` named argument. This call will:
+   1. Perform the necessary spam checks on the model.
+   1. If spam is detected:
+      - Raise a Grape `#error!` exception with a descriptive spam-specific error message.
+      - Include the relevant information added as error fields to the response.
+        For more details on these fields, refer to the section in the REST API documentation on
+        [Resolve requests detected as spam](../../api/index.md#resolve-requests-detected-as-spam).
+
+   NOTE:
+   If you use the standard ApolloLink or Axios interceptor CAPTCHA support described
+   above, you can ignore the field details, because they are handled
+   automatically. They become relevant if you attempt to use the GraphQL API directly to
+   process a failed check for potential spam, and resubmit the request with a solved
+   CAPTCHA response.
+
+Here is an example for the `post` and `put` actions on the `snippets` resource:
+
+```ruby
+module API
+  class Snippets < ::API::Base
+    #...
+    resource :snippets do
+      # This helper provides `#with_captcha_check_rest_api`
+      helpers SpammableActions::CaptchaCheck::RestApiActionsSupport
+
+      post do
+        #...
+        spam_params = ::Spam::SpamParams.new_from_request(request: request)
+        service_response = ::Snippets::CreateService.new(project: nil, current_user: current_user, params: attrs, spam_params: spam_params).execute
+        snippet = service_response.payload[:snippet]
+
+        if service_response.success?
+          present snippet, with: Entities::PersonalSnippet, current_user: current_user
+        else
+          # Wrap the normal error response in a `with_captcha_check_rest_api(spammable: snippet)` block
+          with_captcha_check_rest_api(spammable: snippet) do
+            # If possible spam was detected, an exception would have been thrown by
+            # `#with_captcha_check_rest_api` for Grape to handle via `error!`
+            render_api_error!({ error: service_response.message }, service_response.http_status)
+          end
+        end
+      end
+
+      put ':id' do
+        #...
+        spam_params = ::Spam::SpamParams.new_from_request(request: request)
+        service_response = ::Snippets::UpdateService.new(project: nil, current_user: current_user, params: attrs, spam_params: spam_params).execute(snippet)
+
+        snippet = service_response.payload[:snippet]
+
+        if service_response.success?
+          present snippet, with: Entities::PersonalSnippet, current_user: current_user
+        else
+          # Wrap the normal error response in a `with_captcha_check_rest_api(spammable: snippet)` block
+          with_captcha_check_rest_api(spammable: snippet) do
+            # If possible spam was detected, an exception would have been thrown by
+            # `#with_captcha_check_rest_api` for Grape to handle via `error!`
+            render_api_error!({ error: service_response.message }, service_response.http_status)
+          end
+        end
+      end
+```

doc/development/spam_protection_and_captcha/web_ui.md

@@ -37,7 +37,7 @@ additional fields being added to the models. Instead, communication is handled:
 The spam and CAPTCHA-related logic is also cleanly abstracted into reusable modules and helper methods
 which can wrap existing logic, and only alter the existing flow if potential spam
 is detected or a CAPTCHA display is needed. This approach allows the spam and CAPTCHA
-support to be easily added to new areas of the application with minimal changes to
+support to be added to new areas of the application with minimal changes to
 existing logic. In the case of the frontend, potentially **zero** changes are needed!
 
 On the frontend, this is handled abstractly and transparently using `ApolloLink` for Apollo, and an
@@ -75,7 +75,7 @@ sequenceDiagram
 The backend is also cleanly abstracted via mixin modules and helper methods. The three main
 changes required to the relevant backend controller actions (normally just `create`/`update`) are:
 
-1. Create a `SpamParams` parameter object instance based on the request, using the simple static
+1. Create a `SpamParams` parameter object instance based on the request, using the static
    `#new_from_request` factory method. This method takes a request, and returns a `SpamParams` instance.
 1. Pass the created `SpamParams` instance as the `spam_params` named argument to the
    Service class constructor, which you should have already added. If the spam check indicates