Calls to the API are checked for scope.

- Move the `Oauth2::AccessTokenValidationService` class to
  `AccessTokenValidationService`, since it is now being used for
  personal access token validation as well.

- Each API endpoint declares the scopes it accepts (if any). Currently,
  the top level API module declares the `api` scope, and the `Users` API
  module declares the `read_user` scope (for GET requests).

- Move the `find_user_by_private_token` from the API `Helpers` module to
  the `APIGuard` module, to avoid littering `Helpers` with more
  auth-related methods to support `find_user_by_private_token`

5 files changed, 58 insertions, 30 deletions

diff --git a/lib/api/api.rb b/lib/api/api.rb
index cec2702e44d..9d5adffd8f4 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -3,6 +3,8 @@ module API
     include APIGuard
     version 'v3', using: :path
 
+    before { allow_access_with_scope :api }
+
     rescue_from Gitlab::Access::AccessDeniedError do
       rack_response({ 'message' => '403 Forbidden' }.to_json, 403)
     end
diff --git a/lib/api/api_guard.rb b/lib/api/api_guard.rb
index 8cc7a26f1fa..cd266669b1e 100644
--- a/lib/api/api_guard.rb
+++ b/lib/api/api_guard.rb
@@ -6,6 +6,9 @@ module API
   module APIGuard
     extend ActiveSupport::Concern
 
+    PRIVATE_TOKEN_HEADER = "HTTP_PRIVATE_TOKEN"
+    PRIVATE_TOKEN_PARAM = :private_token
+
     included do |base|
       # OAuth2 Resource Server Authentication
       use Rack::OAuth2::Server::Resource::Bearer, 'The API' do |request|
@@ -41,30 +44,59 @@ module API
       #           Defaults to empty array.
       #
       def doorkeeper_guard(scopes: [])
-        access_token = find_access_token
-        return nil unless access_token
-
-        case validate_access_token(access_token, scopes)
-        when Oauth2::AccessTokenValidationService::INSUFFICIENT_SCOPE
-          raise InsufficientScopeError.new(scopes)
+        if access_token = find_access_token
+          case AccessTokenValidationService.validate(access_token, scopes: scopes)
+          when AccessTokenValidationService::INSUFFICIENT_SCOPE
+            raise InsufficientScopeError.new(scopes)
+          when AccessTokenValidationService::EXPIRED
+            raise ExpiredError
+          when AccessTokenValidationService::REVOKED
+            raise RevokedError
+          when AccessTokenValidationService::VALID
+            @current_user = User.find(access_token.resource_owner_id)
+          end
+        end
+      end
 
-        when Oauth2::AccessTokenValidationService::EXPIRED
-          raise ExpiredError
+      def find_user_by_private_token(scopes: [])
+        token_string = (params[PRIVATE_TOKEN_PARAM] || env[PRIVATE_TOKEN_HEADER]).to_s
 
-        when Oauth2::AccessTokenValidationService::REVOKED
-          raise RevokedError
+        return nil unless token_string.present?
 
-        when Oauth2::AccessTokenValidationService::VALID
-          @current_user = User.find(access_token.resource_owner_id)
-        end
+        find_user_by_authentication_token(token_string) || find_user_by_personal_access_token(token_string, scopes)
       end
 
       def current_user
         @current_user
       end
 
+      # Set the authorization scope(s) allowed for the current request.
+      #
+      # Note: A call to this method adds to any previous scopes in place. This is done because
+      # `Grape` callbacks run from the outside-in: the top-level callback (API::API) runs first, then
+      # the next-level callback (API::API::Users, for example) runs. All these scopes are valid for the
+      # given endpoint (GET `/api/users` is accessible by the `api` and `read_user` scopes), and so they
+      # need to be stored.
+      def allow_access_with_scope(*scopes)
+        @scopes ||= []
+        @scopes.concat(scopes.map(&:to_s))
+      end
+
       private
 
+      def find_user_by_authentication_token(token_string)
+        User.find_by_authentication_token(token_string)
+      end
+
+      def find_user_by_personal_access_token(token_string, scopes)
+        access_token = PersonalAccessToken.active.find_by_token(token_string)
+        return unless access_token
+
+        if AccessTokenValidationService.sufficient_scope?(access_token, scopes)
+          User.find(access_token.user_id)
+        end
+      end
+
       def find_access_token
         @access_token ||= Doorkeeper.authenticate(doorkeeper_request, Doorkeeper.configuration.access_token_methods)
       end
@@ -72,10 +104,6 @@ module API
       def doorkeeper_request
         @doorkeeper_request ||= ActionDispatch::Request.new(env)
       end
-
-      def validate_access_token(access_token, scopes)
-        Oauth2::AccessTokenValidationService.validate(access_token, scopes: scopes)
-      end
     end
 
     module ClassMethods
diff --git a/lib/api/helpers.rb b/lib/api/helpers.rb
index 746849ef4c0..4be659fc20b 100644
--- a/lib/api/helpers.rb
+++ b/lib/api/helpers.rb
@@ -2,8 +2,6 @@ module API
   module Helpers
     include Gitlab::Utils
 
-    PRIVATE_TOKEN_HEADER = "HTTP_PRIVATE_TOKEN"
-    PRIVATE_TOKEN_PARAM = :private_token
     SUDO_HEADER = "HTTP_SUDO"
     SUDO_PARAM = :sudo
 
@@ -308,7 +306,7 @@ module API
     private
 
     def private_token
-      params[PRIVATE_TOKEN_PARAM] || env[PRIVATE_TOKEN_HEADER]
+      params[APIGuard::PRIVATE_TOKEN_PARAM] || env[APIGuard::PRIVATE_TOKEN_HEADER]
     end
 
     def warden
@@ -323,18 +321,11 @@ module API
       warden.try(:authenticate) if %w[GET HEAD].include?(env['REQUEST_METHOD'])
     end
 
-    def find_user_by_private_token
-      token = private_token
-      return nil unless token.present?
-
-      User.find_by_authentication_token(token) || User.find_by_personal_access_token(token)
-    end
-
     def initial_current_user
       return @initial_current_user if defined?(@initial_current_user)
 
-      @initial_current_user ||= find_user_by_private_token
-      @initial_current_user ||= doorkeeper_guard
+      @initial_current_user ||= find_user_by_private_token(scopes: @scopes)
+      @initial_current_user ||= doorkeeper_guard(scopes: @scopes)
       @initial_current_user ||= find_user_from_warden
 
       unless @initial_current_user && Gitlab::UserAccess.new(@initial_current_user).allowed?
diff --git a/lib/api/users.rb b/lib/api/users.rb
index c7db2d71017..0842c3874c5 100644
--- a/lib/api/users.rb
+++ b/lib/api/users.rb
@@ -2,7 +2,10 @@ module API
   class Users < Grape::API
     include PaginationParams
 
-    before { authenticate! }
+    before do
+      allow_access_with_scope :read_user if request.get?
+      authenticate!
+    end
 
     resource :users, requirements: { uid: /[0-9]*/, id: /[0-9]*/ } do
       helpers do
diff --git a/lib/gitlab/auth.rb b/lib/gitlab/auth.rb
index aca5d0020cf..c3c464248ef 100644
--- a/lib/gitlab/auth.rb
+++ b/lib/gitlab/auth.rb
@@ -2,6 +2,10 @@ module Gitlab
   module Auth
     class MissingPersonalTokenError < StandardError; end
 
+    SCOPES = [:api, :read_user]
+    DEFAULT_SCOPES = [:api]
+    OPTIONAL_SCOPES = SCOPES - DEFAULT_SCOPES
+
     class << self
       def find_for_git_client(login, password, project:, ip:)
         raise "Must provide an IP for rate limiting" if ip.nil?