add user scaffold

app/controllers/users_controller.rb

@@ -0,0 +1,53 @@
+class UsersController < ApplicationController
+  before_action :set_user, only: %i[ show update destroy ]
+
+  # GET /users
+  # GET /users.json
+  def index
+    @users = User.all
+  end
+
+  # GET /users/1
+  # GET /users/1.json
+  def show
+  end
+
+  # POST /users
+  # POST /users.json
+  def create
+    @user = User.new(user_params)
+
+    if @user.save
+      render :show, status: :created, location: @user
+    else
+      render json: @user.errors, status: :unprocessable_entity
+    end
+  end
+
+  # PATCH/PUT /users/1
+  # PATCH/PUT /users/1.json
+  def update
+    if @user.update(user_params)
+      render :show, status: :ok, location: @user
+    else
+      render json: @user.errors, status: :unprocessable_entity
+    end
+  end
+
+  # DELETE /users/1
+  # DELETE /users/1.json
+  def destroy
+    @user.destroy
+  end
+
+  private
+    # Use callbacks to share common setup or constraints between actions.
+    def set_user
+      @user = User.find(params[:id])
+    end
+
+    # Only allow a list of trusted parameters through.
+    def user_params
+      params.require(:user).permit(:username)
+    end
+end