Added simple login endpoint with tests for happy and non-happy paths

Makefile

@@ -12,4 +12,6 @@ test:
 run:
 	@bin/rails server
 migrate:
-	@bin/rails db:migrate
+	@bin/rails db:migrate
+create:
+	@bin/rails db:create

app/controllers/api/v1/auth_controller.rb

@@ -19,6 +19,21 @@ def register
         end
       end
 
+      def login
+        user = User.find_by(email: user_params[:email])
+
+        if user&.authenticate(user_params[:password])
+          session = Session.create!(user_id: user.id)
+
+          render json: {
+            token: session.token,
+            user_id: user.id
+          }, status: :ok
+        else
+          render json: { error: "Invalid email or password" }, status: :unauthorized
+        end
+      end
+
       private
       def user_params
         params.require(:user).permit(:email, :password, :password_confirmation)

config/routes.rb

@@ -10,6 +10,7 @@
       # V1 Namespace
       namespace :auth do
         post :register
+        post :login
       end
 
       # Root

test/integration/api/v1/api_v1_auth_login_test.rb

@@ -0,0 +1,68 @@
+require "test_helper"
+
+class ApiV1AuthLoginTest < ActionDispatch::IntegrationTest
+  def setup
+    Session.delete_all
+    User.delete_all
+  end
+
+  test "username and password provided is correct" do
+    user = User.create!(email: "test@example.com", password: "password")
+
+    post "/api/v1/auth/login", params: {
+      user: {
+        email: "test@example.com",
+        password: "password"
+      }
+    }
+
+    assert_response :success
+    body = JSON.parse(response.body)
+    assert body["token"].present?, "expected response to include a session token"
+    assert_equal user.id, body["user_id"]
+  end
+
+  test "session is created upon successful login" do
+    user = User.create!(email: "test@example.com", password: "password")
+
+    assert_difference "Session.count", 1 do
+      post "/api/v1/auth/login", params: {
+        user: {
+          email: "test@example.com",
+          password: "password"
+        }
+      }
+    end
+  end
+
+  test "incorrect password" do
+    User.create!(email: "test@example.com", password: "password")
+
+    post "/api/v1/auth/login", params: {
+      user: {
+        email: "test@example.com",
+        password: "wrongpassword"
+      }
+    }
+
+    assert_response :unauthorized
+  end
+
+  test "non-existent email" do
+    post "/api/v1/auth/login", params: {
+      user: {
+        email: "nonexistent@example.com",
+        password: "password"
+      }
+    }
+
+    assert_response :unauthorized
+  end
+
+  test "missing parameters" do
+    post "/api/v1/auth/login", params: {}
+
+    assert_response :unauthorized
+    assert_equal "Invalid email or password", JSON.parse(response.body)["error"]
+  end
+end