Only allow writing when the access token has permission

app/controllers/concerns/authentication.rb

@@ -59,8 +59,10 @@ module Authentication
       authorization_scheme, bearer_token = request.authorization.to_s.split(" ", 2)
 
       if authorization_scheme == "Bearer" && bearer_token.present?
-        if identity = Identity.find_by_access_token(bearer_token)
-          Current.identity = identity
+        access_token = Identity::AccessToken.find_by(token: bearer_token)
+
+        if access_token && access_token.allows?(request.method)
+          Current.identity = access_token.identity
         else
           head :unauthorized
         end

app/models/identity/access_token.rb

@@ -3,4 +3,8 @@ class Identity::AccessToken < ApplicationRecord
 
   has_secure_token
   enum :permission, %w[ read write ].index_by(&:itself), default: :read
+
+  def allows?(method)
+    method.in?(%w[ GET HEAD ]) || write?
+  end
 end

test/controllers/api_test.rb

@@ -3,6 +3,7 @@ require "test_helper"
 class ApiTest < ActionDispatch::IntegrationTest
   setup do
     @davids_bearer_token = bearer_token_env(identity_access_tokens(:davids_api_token).token)
+    @jasons_bearer_token = bearer_token_env(identity_access_tokens(:jasons_api_token).token)
   end
 
   test "authenticate with valid access token" do
@@ -15,6 +16,14 @@ class ApiTest < ActionDispatch::IntegrationTest
     assert_response :unauthorized
   end
 
+  test "changing data requires a write-endowed access token" do
+    post boards_path(format: :json), params: { board: { name: "My new board" } }, env: @jasons_bearer_token
+    assert_response :unauthorized
+
+    post boards_path(format: :json), params: { board: { name: "My new board" } }, env: @davids_bearer_token
+    assert_response :redirect
+  end
+
   test "boards" do
     get boards_path(format: :json), env: @davids_bearer_token
     assert_equal users(:david).boards.count, @response.parsed_body.count