diff --git a/app/controllers/api/v1/auth_controller.rb b/app/controllers/api/v1/auth_controller.rb
new file mode 100644
index 00000000..9e5e2768
--- /dev/null
+++ b/app/controllers/api/v1/auth_controller.rb
@@ -0,0 +1,210 @@
+module Api
+  module V1
+    class AuthController < BaseController
+      include Invitable
+
+      skip_before_action :authenticate_request!
+      skip_before_action :check_api_key_rate_limit
+      skip_before_action :log_api_access
+
+      def signup
+        # Check if invite code is required
+        if invite_code_required? && params[:invite_code].blank?
+          render json: { error: "Invite code is required" }, status: :forbidden
+          return
+        end
+
+        # Validate invite code if provided
+        if params[:invite_code].present? && !InviteCode.exists?(token: params[:invite_code]&.downcase)
+          render json: { error: "Invalid invite code" }, status: :forbidden
+          return
+        end
+
+        # Validate password
+        password_errors = validate_password(params[:user][:password])
+        if password_errors.any?
+          render json: { errors: password_errors }, status: :unprocessable_entity
+          return
+        end
+
+        # Validate device info
+        unless valid_device_info?
+          render json: { error: "Device information is required" }, status: :bad_request
+          return
+        end
+
+        user = User.new(user_signup_params)
+
+        # Create family for new user
+        family = Family.new
+        user.family = family
+        user.role = :admin
+
+        if user.save
+          # Claim invite code if provided
+          InviteCode.claim!(params[:invite_code]) if params[:invite_code].present?
+
+          # Create device and OAuth token
+          device = create_or_update_device(user)
+          token_response = create_oauth_token_for_device(user, device)
+
+          render json: token_response.merge(
+            user: {
+              id: user.id,
+              email: user.email,
+              first_name: user.first_name,
+              last_name: user.last_name
+            }
+          ), status: :created
+        else
+          render json: { errors: user.errors.full_messages }, status: :unprocessable_entity
+        end
+      end
+
+      def login
+        user = User.find_by(email: params[:email])
+
+        if user&.authenticate(params[:password])
+          # Check MFA if enabled
+          if user.otp_required?
+            unless params[:otp_code].present? && user.verify_otp?(params[:otp_code])
+              render json: {
+                error: "Two-factor authentication required",
+                mfa_required: true
+              }, status: :unauthorized
+              return
+            end
+          end
+
+          # Validate device info
+          unless valid_device_info?
+            render json: { error: "Device information is required" }, status: :bad_request
+            return
+          end
+
+          # Create device and OAuth token
+          device = create_or_update_device(user)
+          token_response = create_oauth_token_for_device(user, device)
+
+          render json: token_response.merge(
+            user: {
+              id: user.id,
+              email: user.email,
+              first_name: user.first_name,
+              last_name: user.last_name
+            }
+          )
+        else
+          render json: { error: "Invalid email or password" }, status: :unauthorized
+        end
+      end
+
+      def refresh
+        # Find the refresh token
+        refresh_token = params[:refresh_token]
+
+        unless refresh_token.present?
+          render json: { error: "Refresh token is required" }, status: :bad_request
+          return
+        end
+
+        # Find the access token associated with this refresh token
+        access_token = Doorkeeper::AccessToken.by_refresh_token(refresh_token)
+
+        if access_token.nil? || access_token.revoked?
+          render json: { error: "Invalid refresh token" }, status: :unauthorized
+          return
+        end
+
+        # Create new access token
+        new_token = Doorkeeper::AccessToken.create!(
+          application: access_token.application,
+          resource_owner_id: access_token.resource_owner_id,
+          expires_in: 30.days.to_i,
+          scopes: access_token.scopes,
+          use_refresh_token: true
+        )
+
+        # Revoke old access token
+        access_token.revoke
+
+        # Update device last seen
+        user = User.find(access_token.resource_owner_id)
+        device = user.mobile_devices.find_by(device_id: params[:device][:device_id])
+        device&.update_last_seen!
+
+        render json: {
+          access_token: new_token.plaintext_token,
+          refresh_token: new_token.plaintext_refresh_token,
+          token_type: "Bearer",
+          expires_in: new_token.expires_in,
+          created_at: new_token.created_at.to_i
+        }
+      end
+
+      private
+
+        def user_signup_params
+          params.require(:user).permit(:email, :password, :first_name, :last_name)
+        end
+
+        def validate_password(password)
+          errors = []
+
+          if password.blank?
+            errors << "Password can't be blank"
+            return errors
+          end
+
+          errors << "Password must be at least 8 characters" if password.length < 8
+          errors << "Password must include both uppercase and lowercase letters" unless password.match?(/[A-Z]/) && password.match?(/[a-z]/)
+          errors << "Password must include at least one number" unless password.match?(/\d/)
+          errors << "Password must include at least one special character" unless password.match?(/[!@#$%^&*(),.?":{}|<>]/)
+
+          errors
+        end
+
+        def valid_device_info?
+          device = params[:device]
+          return false if device.nil?
+
+          required_fields = %w[device_id device_name device_type os_version app_version]
+          required_fields.all? { |field| device[field].present? }
+        end
+
+        def create_or_update_device(user)
+          # Handle both string and symbol keys
+          device_data = params[:device].permit(:device_id, :device_name, :device_type, :os_version, :app_version)
+          
+          device = user.mobile_devices.find_or_initialize_by(device_id: device_data[:device_id])
+          device.update!(device_data.merge(last_seen_at: Time.current))
+          device
+        end
+
+        def create_oauth_token_for_device(user, device)
+          # Create OAuth application for this device if needed
+          oauth_app = device.create_oauth_application!
+
+          # Revoke any existing tokens for this device
+          device.revoke_all_tokens!
+
+          # Create new access token with 30-day expiration
+          access_token = Doorkeeper::AccessToken.create!(
+            application: oauth_app,
+            resource_owner_id: user.id,
+            expires_in: 30.days.to_i,
+            scopes: "read_write",
+            use_refresh_token: true
+          )
+
+          {
+            access_token: access_token.plaintext_token,
+            refresh_token: access_token.plaintext_refresh_token,
+            token_type: "Bearer",
+            expires_in: access_token.expires_in,
+            created_at: access_token.created_at.to_i
+          }
+        end
+    end
+  end
+end
diff --git a/app/controllers/api/v1/base_controller.rb b/app/controllers/api/v1/base_controller.rb
index afc3f4f3..a9b577d1 100644
--- a/app/controllers/api/v1/base_controller.rb
+++ b/app/controllers/api/v1/base_controller.rb
@@ -6,6 +6,9 @@ class Api::V1::BaseController < ApplicationController
   # Skip regular session-based authentication for API
   skip_authentication
 
+  # Skip CSRF protection for API endpoints
+  skip_before_action :verify_authenticity_token
+
   # Skip onboarding requirements for API endpoints
   skip_before_action :require_onboarding_and_upgrade
 
diff --git a/app/models/api_key.rb b/app/models/api_key.rb
index 474712fa..e966c7f6 100644
--- a/app/models/api_key.rb
+++ b/app/models/api_key.rb
@@ -4,12 +4,16 @@ class ApiKey < ApplicationRecord
   # Use Rails built-in encryption for secure storage
   encrypts :display_key, deterministic: true
 
+  # Constants
+  SOURCES = [ "web", "mobile" ].freeze
+
   # Validations
   validates :display_key, presence: true, uniqueness: true
   validates :name, presence: true
   validates :scopes, presence: true
+  validates :source, presence: true, inclusion: { in: SOURCES }
   validate :scopes_not_empty
-  validate :one_active_key_per_user, on: :create
+  validate :one_active_key_per_user_per_source, on: :create
 
   # Callbacks
   before_validation :set_display_key
@@ -82,9 +86,9 @@ class ApiKey < ApplicationRecord
       end
     end
 
-    def one_active_key_per_user
-      if user&.api_keys&.active&.where&.not(id: id)&.exists?
-        errors.add(:user, "can only have one active API key")
+    def one_active_key_per_user_per_source
+      if user&.api_keys&.active&.where(source: source)&.where&.not(id: id)&.exists?
+        errors.add(:user, "can only have one active API key per source (#{source})")
       end
     end
 end
diff --git a/app/models/mobile_device.rb b/app/models/mobile_device.rb
new file mode 100644
index 00000000..106b2928
--- /dev/null
+++ b/app/models/mobile_device.rb
@@ -0,0 +1,55 @@
+class MobileDevice < ApplicationRecord
+  belongs_to :user
+  belongs_to :oauth_application, class_name: "Doorkeeper::Application", optional: true
+
+  validates :device_id, presence: true, uniqueness: { scope: :user_id }
+  validates :device_name, presence: true
+  validates :device_type, presence: true, inclusion: { in: %w[ios android] }
+
+  before_validation :set_last_seen_at, on: :create
+
+  scope :active, -> { where("last_seen_at > ?", 90.days.ago) }
+
+  def active?
+    last_seen_at > 90.days.ago
+  end
+
+  def update_last_seen!
+    update_column(:last_seen_at, Time.current)
+  end
+
+  def create_oauth_application!
+    return oauth_application if oauth_application.present?
+
+    app = Doorkeeper::Application.create!(
+      name: "Mobile App - #{device_id}",
+      redirect_uri: "maybe://oauth/callback", # Custom scheme for mobile
+      scopes: "read_write", # Use the configured scope
+      confidential: false # Public client for mobile
+    )
+    
+    # Store the association
+    update!(oauth_application: app)
+    app
+  end
+
+  def active_tokens
+    return Doorkeeper::AccessToken.none unless oauth_application
+    
+    Doorkeeper::AccessToken
+      .where(application: oauth_application)
+      .where(resource_owner_id: user_id)
+      .where(revoked_at: nil)
+      .where("expires_in IS NULL OR created_at + expires_in * interval '1 second' > ?", Time.current)
+  end
+
+  def revoke_all_tokens!
+    active_tokens.update_all(revoked_at: Time.current)
+  end
+
+  private
+
+    def set_last_seen_at
+      self.last_seen_at ||= Time.current
+    end
+end
diff --git a/app/models/user.rb b/app/models/user.rb
index d391e62b..501e95b8 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -6,6 +6,7 @@ class User < ApplicationRecord
   has_many :sessions, dependent: :destroy
   has_many :chats, dependent: :destroy
   has_many :api_keys, dependent: :destroy
+  has_many :mobile_devices, dependent: :destroy
   has_many :invitations, foreign_key: :inviter_id, dependent: :destroy
   has_many :impersonator_support_sessions, class_name: "ImpersonationSession", foreign_key: :impersonator_id, dependent: :destroy
   has_many :impersonated_support_sessions, class_name: "ImpersonationSession", foreign_key: :impersonated_id, dependent: :destroy
diff --git a/config/initializers/doorkeeper.rb b/config/initializers/doorkeeper.rb
index 2a400288..9fe01849 100644
--- a/config/initializers/doorkeeper.rb
+++ b/config/initializers/doorkeeper.rb
@@ -255,7 +255,7 @@ Doorkeeper.configure do
   # NOTE: you must also run the rails g doorkeeper:application_owner generator
   # to provide the necessary support
   #
-  # enable_application_owner confirmation: false
+  enable_application_owner confirmation: false
 
   # Define access token scopes for your provider
   # For more information go to
diff --git a/config/routes.rb b/config/routes.rb
index d352a5a8..8d0976c8 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -185,6 +185,11 @@ Rails.application.routes.draw do
   # API routes
   namespace :api do
     namespace :v1 do
+      # Authentication endpoints
+      post "auth/signup", to: "auth#signup"
+      post "auth/login", to: "auth#login"
+      post "auth/refresh", to: "auth#refresh"
+      
       # Production API endpoints
       resources :accounts, only: [ :index ]
       resources :transactions, only: [ :index, :show, :create, :update, :destroy ]
diff --git a/db/migrate/20250618104425_add_source_to_api_keys.rb b/db/migrate/20250618104425_add_source_to_api_keys.rb
new file mode 100644
index 00000000..e773494d
--- /dev/null
+++ b/db/migrate/20250618104425_add_source_to_api_keys.rb
@@ -0,0 +1,6 @@
+class AddSourceToApiKeys < ActiveRecord::Migration[7.2]
+  def change
+    add_column :api_keys, :source, :string, default: "web"
+    add_index :api_keys, [:user_id, :source]
+  end
+end
diff --git a/db/migrate/20250618110104_create_mobile_devices.rb b/db/migrate/20250618110104_create_mobile_devices.rb
new file mode 100644
index 00000000..6875e978
--- /dev/null
+++ b/db/migrate/20250618110104_create_mobile_devices.rb
@@ -0,0 +1,17 @@
+class CreateMobileDevices < ActiveRecord::Migration[7.2]
+  def change
+    create_table :mobile_devices, id: :uuid do |t|
+      t.references :user, null: false, foreign_key: true, type: :uuid
+      t.string :device_id
+      t.string :device_name
+      t.string :device_type
+      t.string :os_version
+      t.string :app_version
+      t.datetime :last_seen_at
+
+      t.timestamps
+    end
+    add_index :mobile_devices, :device_id, unique: true
+    add_index :mobile_devices, [:user_id, :device_id], unique: true
+  end
+end
diff --git a/db/migrate/20250618110736_add_owner_to_oauth_applications.rb b/db/migrate/20250618110736_add_owner_to_oauth_applications.rb
new file mode 100644
index 00000000..26b03049
--- /dev/null
+++ b/db/migrate/20250618110736_add_owner_to_oauth_applications.rb
@@ -0,0 +1,7 @@
+class AddOwnerToOauthApplications < ActiveRecord::Migration[7.2]
+  def change
+    add_column :oauth_applications, :owner_id, :uuid
+    add_column :oauth_applications, :owner_type, :string
+    add_index :oauth_applications, [:owner_id, :owner_type]
+  end
+end
diff --git a/db/migrate/20250618120703_add_oauth_application_to_mobile_devices.rb b/db/migrate/20250618120703_add_oauth_application_to_mobile_devices.rb
new file mode 100644
index 00000000..391f8c81
--- /dev/null
+++ b/db/migrate/20250618120703_add_oauth_application_to_mobile_devices.rb
@@ -0,0 +1,6 @@
+class AddOauthApplicationToMobileDevices < ActiveRecord::Migration[7.2]
+  def change
+    add_column :mobile_devices, :oauth_application_id, :integer
+    add_index :mobile_devices, :oauth_application_id
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 95ed2ec6..e817a168 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2025_06_13_152743) do
+ActiveRecord::Schema[7.2].define(version: 2025_06_18_110736) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
   enable_extension "plpgsql"
@@ -98,8 +98,10 @@ ActiveRecord::Schema[7.2].define(version: 2025_06_13_152743) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "display_key", null: false
+    t.string "source", default: "web"
     t.index ["display_key"], name: "index_api_keys_on_display_key", unique: true
     t.index ["revoked_at"], name: "index_api_keys_on_revoked_at"
+    t.index ["user_id", "source"], name: "index_api_keys_on_user_id_and_source"
     t.index ["user_id"], name: "index_api_keys_on_user_id"
   end
 
@@ -429,6 +431,21 @@ ActiveRecord::Schema[7.2].define(version: 2025_06_13_152743) do
     t.index ["chat_id"], name: "index_messages_on_chat_id"
   end
 
+  create_table "mobile_devices", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
+    t.uuid "user_id", null: false
+    t.string "device_id"
+    t.string "device_name"
+    t.string "device_type"
+    t.string "os_version"
+    t.string "app_version"
+    t.datetime "last_seen_at"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["device_id"], name: "index_mobile_devices_on_device_id", unique: true
+    t.index ["user_id", "device_id"], name: "index_mobile_devices_on_user_id_and_device_id", unique: true
+    t.index ["user_id"], name: "index_mobile_devices_on_user_id"
+  end
+
   create_table "oauth_access_grants", force: :cascade do |t|
     t.string "resource_owner_id", null: false
     t.bigint "application_id", null: false
@@ -468,6 +485,9 @@ ActiveRecord::Schema[7.2].define(version: 2025_06_13_152743) do
     t.boolean "confidential", default: true, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.uuid "owner_id"
+    t.string "owner_type"
+    t.index ["owner_id", "owner_type"], name: "index_oauth_applications_on_owner_id_and_owner_type"
     t.index ["uid"], name: "index_oauth_applications_on_uid", unique: true
   end
 
@@ -802,6 +822,7 @@ ActiveRecord::Schema[7.2].define(version: 2025_06_13_152743) do
   add_foreign_key "invitations", "users", column: "inviter_id"
   add_foreign_key "merchants", "families"
   add_foreign_key "messages", "chats"
+  add_foreign_key "mobile_devices", "users"
   add_foreign_key "oauth_access_grants", "oauth_applications", column: "application_id"
   add_foreign_key "oauth_access_tokens", "oauth_applications", column: "application_id"
   add_foreign_key "plaid_accounts", "plaid_items"
diff --git a/test/controllers/api/v1/auth_controller_test.rb b/test/controllers/api/v1/auth_controller_test.rb
new file mode 100644
index 00000000..9c021387
--- /dev/null
+++ b/test/controllers/api/v1/auth_controller_test.rb
@@ -0,0 +1,410 @@
+require "test_helper"
+
+class Api::V1::AuthControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    # Clean up any existing invite codes
+    InviteCode.destroy_all
+    @device_info = {
+      device_id: "test-device-123",
+      device_name: "Test iPhone",
+      device_type: "ios",
+      os_version: "17.0",
+      app_version: "1.0.0"
+    }
+  end
+
+  test "should signup new user and return OAuth tokens" do
+    assert_difference("User.count", 1) do
+      assert_difference("MobileDevice.count", 1) do
+        assert_difference("Doorkeeper::Application.count", 1) do
+          assert_difference("Doorkeeper::AccessToken.count", 1) do
+            post "/api/v1/auth/signup", params: {
+              user: {
+                email: "newuser@example.com",
+                password: "SecurePass123!",
+                first_name: "New",
+                last_name: "User"
+              },
+              device: @device_info
+            }
+          end
+        end
+      end
+    end
+
+    assert_response :created
+    response_data = JSON.parse(response.body)
+
+    assert response_data["user"]["id"].present?
+    assert_equal "newuser@example.com", response_data["user"]["email"]
+    assert_equal "New", response_data["user"]["first_name"]
+    assert_equal "User", response_data["user"]["last_name"]
+    
+    # OAuth token assertions
+    assert response_data["access_token"].present?
+    assert response_data["refresh_token"].present?
+    assert_equal "Bearer", response_data["token_type"]
+    assert_equal 2592000, response_data["expires_in"] # 30 days
+    assert response_data["created_at"].present?
+
+    # Verify the device was created
+    new_user = User.find(response_data["user"]["id"])
+    device = new_user.mobile_devices.first
+    assert_equal @device_info[:device_id], device.device_id
+    assert_equal @device_info[:device_name], device.device_name
+    assert_equal @device_info[:device_type], device.device_type
+  end
+
+  test "should not signup without device info" do
+    assert_no_difference("User.count") do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: "newuser@example.com",
+          password: "SecurePass123!",
+          first_name: "New",
+          last_name: "User"
+        }
+      }
+    end
+
+    assert_response :bad_request
+    response_data = JSON.parse(response.body)
+    assert_equal "Device information is required", response_data["error"]
+  end
+
+  test "should not signup with invalid password" do
+    assert_no_difference("User.count") do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: "newuser@example.com",
+          password: "weak",
+          first_name: "New",
+          last_name: "User"
+        },
+        device: @device_info
+      }
+    end
+
+    assert_response :unprocessable_entity
+    response_data = JSON.parse(response.body)
+    assert response_data["errors"].include?("Password must be at least 8 characters")
+  end
+
+  test "should not signup with duplicate email" do
+    existing_user = users(:family_admin)
+
+    assert_no_difference("User.count") do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: existing_user.email,
+          password: "SecurePass123!",
+          first_name: "Duplicate",
+          last_name: "User"
+        },
+        device: @device_info
+      }
+    end
+
+    assert_response :unprocessable_entity
+  end
+
+  test "should create user with admin role and family" do
+    post "/api/v1/auth/signup", params: {
+      user: {
+        email: "newuser@example.com",
+        password: "SecurePass123!",
+        first_name: "New",
+        last_name: "User"
+      },
+      device: @device_info
+    }
+
+    assert_response :created
+    response_data = JSON.parse(response.body)
+
+    new_user = User.find(response_data["user"]["id"])
+    assert_equal "admin", new_user.role
+    assert new_user.family.present?
+  end
+
+  test "should require invite code when enabled" do
+    # Mock invite code requirement
+    Api::V1::AuthController.any_instance.stubs(:invite_code_required?).returns(true)
+
+    assert_no_difference("User.count") do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: "newuser@example.com",
+          password: "SecurePass123!",
+          first_name: "New",
+          last_name: "User"
+        },
+        device: @device_info
+      }
+    end
+
+    assert_response :forbidden
+    response_data = JSON.parse(response.body)
+    assert_equal "Invite code is required", response_data["error"]
+  end
+
+  test "should signup with valid invite code when required" do
+    # Create a valid invite code
+    invite_code = InviteCode.create!
+
+    # Mock invite code requirement
+    Api::V1::AuthController.any_instance.stubs(:invite_code_required?).returns(true)
+
+    assert_difference("User.count", 1) do
+      assert_difference("InviteCode.count", -1) do
+        post "/api/v1/auth/signup", params: {
+          user: {
+            email: "newuser@example.com",
+            password: "SecurePass123!",
+            first_name: "New",
+            last_name: "User"
+          },
+          device: @device_info,
+          invite_code: invite_code.token
+        }
+      end
+    end
+
+    assert_response :created
+  end
+
+  test "should reject invalid invite code" do
+    # Mock invite code requirement
+    Api::V1::AuthController.any_instance.stubs(:invite_code_required?).returns(false)
+
+    assert_no_difference("User.count") do
+      post "/api/v1/auth/signup", params: {
+        user: {
+          email: "newuser@example.com",
+          password: "SecurePass123!",
+          first_name: "New",
+          last_name: "User"
+        },
+        device: @device_info,
+        invite_code: "invalid_code"
+      }
+    end
+
+    assert_response :forbidden
+    response_data = JSON.parse(response.body)
+    assert_equal "Invalid invite code", response_data["error"]
+  end
+
+  test "should login existing user and return OAuth tokens" do
+    user = users(:family_admin)
+    password = user_password_test
+
+    # Ensure user has no mobile devices
+    user.mobile_devices.destroy_all
+
+    assert_difference("MobileDevice.count", 1) do
+      assert_difference("Doorkeeper::AccessToken.count", 1) do
+        post "/api/v1/auth/login", params: {
+          email: user.email,
+          password: password,
+          device: @device_info
+        }
+      end
+    end
+
+    assert_response :success
+    response_data = JSON.parse(response.body)
+
+    assert_equal user.id.to_s, response_data["user"]["id"]
+    assert_equal user.email, response_data["user"]["email"]
+    
+    # OAuth token assertions
+    assert response_data["access_token"].present?
+    assert response_data["refresh_token"].present?
+    assert_equal "Bearer", response_data["token_type"]
+    assert_equal 2592000, response_data["expires_in"] # 30 days
+
+    # Verify the device
+    device = user.mobile_devices.where(device_id: @device_info[:device_id]).first
+    assert device.present?
+    assert device.active?
+  end
+
+  test "should require MFA when enabled" do
+    user = users(:family_admin)
+    password = user_password_test
+
+    # Enable MFA for user
+    user.setup_mfa!
+    user.enable_mfa!
+
+    post "/api/v1/auth/login", params: {
+      email: user.email,
+      password: password,
+      device: @device_info
+    }
+
+    assert_response :unauthorized
+    response_data = JSON.parse(response.body)
+    assert_equal "Two-factor authentication required", response_data["error"]
+    assert response_data["mfa_required"]
+  end
+
+  test "should login with valid MFA code" do
+    user = users(:family_admin)
+    password = user_password_test
+
+    # Enable MFA for user
+    user.setup_mfa!
+    user.enable_mfa!
+    totp = ROTP::TOTP.new(user.otp_secret)
+
+    assert_difference("Doorkeeper::AccessToken.count", 1) do
+      post "/api/v1/auth/login", params: {
+        email: user.email,
+        password: password,
+        otp_code: totp.now,
+        device: @device_info
+      }
+    end
+
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert response_data["access_token"].present?
+  end
+
+  test "should revoke existing tokens for same device on login" do
+    user = users(:family_admin)
+    password = user_password_test
+
+    # Create an existing device and token
+    device = user.mobile_devices.create!(@device_info)
+    oauth_app = device.create_oauth_application!
+    existing_token = Doorkeeper::AccessToken.create!(
+      application: oauth_app,
+      resource_owner_id: user.id,
+      expires_in: 30.days.to_i,
+      scopes: "read_write"
+    )
+
+    assert existing_token.accessible?
+
+    post "/api/v1/auth/login", params: {
+      email: user.email,
+      password: password,
+      device: @device_info
+    }
+
+    assert_response :success
+
+    # Check that old token was revoked
+    existing_token.reload
+    assert existing_token.revoked?
+  end
+
+  test "should not login with invalid password" do
+    user = users(:family_admin)
+
+    assert_no_difference("Doorkeeper::AccessToken.count") do
+      post "/api/v1/auth/login", params: {
+        email: user.email,
+        password: "wrong_password",
+        device: @device_info
+      }
+    end
+
+    assert_response :unauthorized
+    response_data = JSON.parse(response.body)
+    assert_equal "Invalid email or password", response_data["error"]
+  end
+
+  test "should not login with non-existent email" do
+    assert_no_difference("Doorkeeper::AccessToken.count") do
+      post "/api/v1/auth/login", params: {
+        email: "nonexistent@example.com",
+        password: user_password_test,
+        device: @device_info
+      }
+    end
+
+    assert_response :unauthorized
+    response_data = JSON.parse(response.body)
+    assert_equal "Invalid email or password", response_data["error"]
+  end
+
+  test "should not login without device info" do
+    user = users(:family_admin)
+
+    assert_no_difference("Doorkeeper::AccessToken.count") do
+      post "/api/v1/auth/login", params: {
+        email: user.email,
+        password: user_password_test
+      }
+    end
+
+    assert_response :bad_request
+    response_data = JSON.parse(response.body)
+    assert_equal "Device information is required", response_data["error"]
+  end
+
+  test "should refresh access token with valid refresh token" do
+    user = users(:family_admin)
+    device = user.mobile_devices.create!(@device_info)
+    oauth_app = device.create_oauth_application!
+    
+    # Create initial token
+    initial_token = Doorkeeper::AccessToken.create!(
+      application: oauth_app,
+      resource_owner_id: user.id,
+      expires_in: 30.days.to_i,
+      scopes: "read_write",
+      use_refresh_token: true
+    )
+
+    # Wait to ensure different timestamps
+    sleep 0.1
+
+    assert_difference("Doorkeeper::AccessToken.count", 1) do
+      post "/api/v1/auth/refresh", params: {
+        refresh_token: initial_token.refresh_token,
+        device: @device_info
+      }
+    end
+
+    assert_response :success
+    response_data = JSON.parse(response.body)
+
+    # New token assertions
+    assert response_data["access_token"].present?
+    assert response_data["refresh_token"].present?
+    assert_not_equal initial_token.token, response_data["access_token"]
+    assert_equal 2592000, response_data["expires_in"]
+
+    # Old token should be revoked
+    initial_token.reload
+    assert initial_token.revoked?
+  end
+
+  test "should not refresh with invalid refresh token" do
+    assert_no_difference("Doorkeeper::AccessToken.count") do
+      post "/api/v1/auth/refresh", params: {
+        refresh_token: "invalid_token",
+        device: @device_info
+      }
+    end
+
+    assert_response :unauthorized
+    response_data = JSON.parse(response.body)
+    assert_equal "Invalid refresh token", response_data["error"]
+  end
+
+  test "should not refresh without refresh token" do
+    post "/api/v1/auth/refresh", params: {
+      device: @device_info
+    }
+
+    assert_response :bad_request
+    response_data = JSON.parse(response.body)
+    assert_equal "Refresh token is required", response_data["error"]
+  end
+end
\ No newline at end of file
diff --git a/test/fixtures/mobile_devices.yml b/test/fixtures/mobile_devices.yml
new file mode 100644
index 00000000..28dc37ea
--- /dev/null
+++ b/test/fixtures/mobile_devices.yml
@@ -0,0 +1,3 @@
+# Read about fixtures at https://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
+
+# Empty fixtures to avoid conflicts
\ No newline at end of file
diff --git a/test/models/mobile_device_test.rb b/test/models/mobile_device_test.rb
new file mode 100644
index 00000000..79bb8f62
--- /dev/null
+++ b/test/models/mobile_device_test.rb
@@ -0,0 +1,7 @@
+require "test_helper"
+
+class MobileDeviceTest < ActiveSupport::TestCase
+  # test "the truth" do
+  #   assert true
+  # end
+end