Store per-device user agent for remoteStorage authorizations

- Add user_agent to remote_storage_authorizations and rs_authorization_codes
- Capture the browser's user agent at consent, carry it on the authorization
  code, and store it on the authorization when the code is exchanged
- Store it directly for the implicit flow too

With the reuse shortcut gone, each authorization is already a distinct
per-device token; this adds the metadata needed to label and display them.

Part of #254

app/controllers/rs/oauth_controller.rb

@@ -104,6 +104,7 @@ class Rs::OauthController < ApplicationController
         redirect_uri: redirect_uri,
         permissions: permissions,
         expire_at: expire_at,
+        user_agent: request.user_agent,
         code_challenge: challenge,
         code_challenge_method: method
       )
@@ -116,7 +117,8 @@ class Rs::OauthController < ApplicationController
         client_id: client_id,
         redirect_uri: redirect_uri,
         app_name: client_id,
-        expire_at: expire_at
+        expire_at: expire_at,
+        user_agent: request.user_agent
       )
 
       redirect_to url_with_state("#{redirect_uri}#access_token=#{auth.token}", state),

app/services/rs_oauth_manager/exchange_code.rb

@@ -25,7 +25,8 @@ module RsOauthManager
         client_id: auth_code.client_id,
         redirect_uri: auth_code.redirect_uri,
         app_name: auth_code.client_id,
-        expire_at: auth_code.permission_expire_at
+        expire_at: auth_code.permission_expire_at,
+        user_agent: auth_code.user_agent
       )
 
       auth_code.consume!

app/services/rs_oauth_manager/issue_code.rb

@@ -2,7 +2,7 @@ module RsOauthManager
   class IssueCode < RsOauthManagerService
     def initialize(user:, client_id:, redirect_uri:, permissions:,
                    code_challenge:, code_challenge_method: "S256",
-                   expire_at: nil)
+                   expire_at: nil, user_agent: nil)
       @user = user
       @client_id = client_id
       @redirect_uri = redirect_uri
@@ -10,6 +10,7 @@ module RsOauthManager
       @code_challenge = code_challenge
       @code_challenge_method = code_challenge_method
       @expire_at = expire_at
+      @user_agent = user_agent
     end
 
     def call
@@ -19,6 +20,7 @@ module RsOauthManager
         redirect_uri: @redirect_uri,
         permissions: @permissions,
         permission_expire_at: @expire_at,
+        user_agent: @user_agent,
         code_challenge: @code_challenge,
         code_challenge_method: @code_challenge_method
       )

db/migrate/20261102130000_add_user_agent_to_rs_authorizations.rb

@@ -0,0 +1,6 @@
+class AddUserAgentToRsAuthorizations < ActiveRecord::Migration[8.1]
+  def change
+    add_column :remote_storage_authorizations, :user_agent, :string
+    add_column :rs_authorization_codes, :user_agent, :string
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_11_02_120000) do
+ActiveRecord::Schema[8.1].define(version: 2026_11_02_130000) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.bigint "blob_id", null: false
     t.datetime "created_at", null: false
@@ -110,6 +110,7 @@ ActiveRecord::Schema[8.1].define(version: 2026_11_02_120000) do
     t.string "redirect_uri"
     t.string "token"
     t.datetime "updated_at", null: false
+    t.string "user_agent"
     t.integer "user_id", null: false
     t.integer "web_app_id"
     t.index ["permissions"], name: "index_remote_storage_authorizations_on_permissions"
@@ -128,6 +129,7 @@ ActiveRecord::Schema[8.1].define(version: 2026_11_02_120000) do
     t.text "permissions", default: "--- []\n"
     t.string "redirect_uri", null: false
     t.datetime "updated_at", null: false
+    t.string "user_agent"
     t.integer "user_id", null: false
     t.index ["code_digest"], name: "index_rs_authorization_codes_on_code_digest", unique: true
     t.index ["user_id"], name: "index_rs_authorization_codes_on_user_id"

spec/controllers/rs/oauth_controller_spec.rb

@@ -310,6 +310,7 @@ RSpec.describe Rs::OauthController, type: :controller do
     context "when user is signed in" do
       before do
         sign_in user
+        request.user_agent = "RSpec Device"
       end
 
       after do
@@ -334,6 +335,10 @@ RSpec.describe Rs::OauthController, type: :controller do
           expect(@auth.permissions).to eq(%w(documents photos contacts:rw videos:r tasks/work:r))
         end
 
+        it "stores the device's user agent" do
+          expect(@auth.user_agent).to eq("RSpec Device")
+        end
+
         it "redirects to the redirect_uri" do
           expect(response).to redirect_to("https://example.com#access_token=#{@auth.token}&state=foobar123")
         end
@@ -463,6 +468,7 @@ RSpec.describe Rs::OauthController, type: :controller do
           expect(@code.permissions).to eq(%w(documents photos contacts:rw))
           expect(@code.code_challenge).to eq("challenge123")
           expect(@code.code_challenge_method).to eq("S256")
+          expect(@code.user_agent).to eq("RSpec Device")
         end
 
         it "does not create a remote storage authorization" do

spec/services/rs_oauth_manager/exchange_code_spec.rb

@@ -20,6 +20,7 @@ RSpec.describe RsOauthManager::ExchangeCode do
       permissions: %w(documents:rw),
       code_challenge: code_challenge,
       code_challenge_method: "S256",
+      user_agent: "RSpec Device",
       **overrides
     )
   end
@@ -43,6 +44,7 @@ RSpec.describe RsOauthManager::ExchangeCode do
     expect(auth.permissions).to eq(%w(documents:rw))
     expect(auth.client_id).to eq("example.com")
     expect(auth.token).to be_present
+    expect(auth.user_agent).to eq("RSpec Device")
     expect(RsAuthorizationCode.exists?(code.id)).to be(false)
   end
 

spec/services/rs_oauth_manager/issue_code_spec.rb

@@ -11,7 +11,8 @@ RSpec.describe RsOauthManager::IssueCode do
       permissions: %w(documents:rw),
       code_challenge: "challenge",
       code_challenge_method: "S256",
-      expire_at: 1.month.from_now
+      expire_at: 1.month.from_now,
+      user_agent: "RSpec Device"
     )
   end
 
@@ -21,6 +22,7 @@ RSpec.describe RsOauthManager::IssueCode do
     expect(subject.client_id).to eq("example.com")
     expect(subject.permissions).to eq(%w(documents:rw))
     expect(subject.code_challenge).to eq("challenge")
+    expect(subject.user_agent).to eq("RSpec Device")
   end
 
   it "does not create a remote storage authorization" do