chore: update MySQL notebook to use auto IAM AuthN (GoogleCloudPlatform#576)

Author: jackwotherspoon

samples/notebooks/mysql_python_connector.ipynb

@@ -584,9 +584,9 @@
       "source": [
         "### 🪪  IAM Database Authentication \n",
         "\n",
-        "[Manual IAM database authentication](https://cloud.google.com/sql/docs/mysql/authentication#manual) is supported for **MySQL** Cloud SQL instances. \n",
+        "[Automatic IAM database authentication](https://cloud.google.com/sql/docs/mysql/authentication#automatic) is supported for **MySQL** Cloud SQL instances. \n",
         "\n",
-        "> 💡 This allows an IAM user to establish an authenticated connection to a MySQL database using an **OAuth2** token as their password in the connector's `connect` method.\n",
+        "> 💡 This allows an IAM user to establish an authenticated connection to a MySQL database without having to set a password and enabling the `enable_iam_auth` parameter in the connector's `connect` method.\n",
         "\n",
         "> 🚨 If you are using a pre-existing Cloud SQL instance within this notebook you may need to [configure Cloud SQL instance to allow IAM authentication](https://cloud.google.com/sql/docs/mysql/create-edit-iam-instances#configuring_existing_instances_for) by setting the `cloudsql_iam_authentication` database flag to `On`. \n",
         "(Cloud SQL instances created within this notebook already have it enabled)\n"
@@ -663,28 +663,20 @@
         "import sqlalchemy\n",
         "\n",
         "# IAM database user parameter (IAM user's email before the \"@\" sign, mysql truncates usernames)\n",
-        "# ex. IAM user with email \"[email protected]\" would have database user name \"demo-user\"\n",
+        "# ex. IAM user with email \"[email protected]\" would have database username \"demo-user\"\n",
         "IAM_USER = current_user[0].split(\"@\")[0]\n",
         "\n",
-        "# get application default credentials of IAM user (current logged in user)\n",
-        "credentials, project = google.auth.default()\n",
-        "\n",
-        "# refresh credentials if expired\n",
-        "if not credentials.valid:\n",
-        "      request = Request()\n",
-        "      credentials.refresh(request)\n",
-        "\n",
         "# initialize connector\n",
         "connector = Connector()\n",
         "\n",
-        "# getconn now using IAM user and OAuth2 token as password\n",
+        "# getconn now using IAM user and requiring no password with IAM Auth enabled\n",
         "def getconn():\n",
         "    conn = connector.connect(\n",
         "      INSTANCE_CONNECTION_NAME,\n",
         "      \"pymysql\",\n",
         "      user=IAM_USER,\n",
-        "      password=credentials.token,\n",
         "      db=\"\", # log in to instance but don't connect to specific database\n",
+        "      enable_iam_auth=True\n",
         "    )\n",
         "    return conn\n",
         "\n",