Begin by accessing the Google Cloud Console. Create a new project or select an existing one. Navigate to "APIs & Services" and enable the "Admin SDK" API, which includes the Google Directory API. Create OAuth 2.0 credentials by setting up a new client ID under "Credentials" for a desktop application, and ensure you download the JSON file containing your client secrets.

Open your terminal or command prompt and install the necessary Python libraries. This includes `google-auth`, `google-auth-oauthlib`, `google-auth-httplib2`, and `google-api-python-client` using pip. These libraries will allow you to authenticate and interact with the Google Directory API.

```bash
pip install google-auth google-auth-oauthlib google-auth-httplib2 google-api-python-client pymongo
```

Create a Python script to authenticate and access the Google Directory. Use the OAuth 2.0 credentials JSON file to authenticate. Load the Google Directory service using the `build` function from `googleapiclient.discovery`. Ensure you have the right scopes, such as `https://www.googleapis.com/auth/admin.directory.user.readonly`.

```python
from google.oauth2 import service_account
from googleapiclient.discovery import build

SCOPES = ['https://www.googleapis.com/auth/admin.directory.user.readonly']
SERVICE_ACCOUNT_FILE = 'path/to/your/service-account-file.json'

credentials = service_account.Credentials.from_service_account_file(
SERVICE_ACCOUNT_FILE, scopes=SCOPES)

service = build('admin', 'directory_v1', credentials=credentials)
```

Use the authenticated service object to fetch data. For example, to get a list of users, utilize the `service.users().list()` method. Handle pagination to retrieve all data if necessary.

```python
results = service.users().list(customer='my_customer', maxResults=200).execute()
users = results.get('users', [])
```

Ensure MongoDB is installed and running on your machine or accessible via a network. Create or select a database and collection where the Google Directory data will be stored. Use the `pymongo` library to interact with MongoDB.

```python
from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')
db = client['your_database_name']
collection = db['your_collection_name']
```

Process the data fetched from Google Directory to match the structure expected by MongoDB. You might need to clean or transform fields to ensure data consistency and integrity.

```python
prepared_data = []
for user in users:
user_data = {
'id': user.get('id'),
'name': user.get('name').get('fullName'),
'email': user.get('primaryEmail'),
# Add additional fields as necessary
}
prepared_data.append(user_data)
```

Use the `insert_many()` method from `pymongo` to insert the prepared data into the MongoDB collection. Confirm successful insertion by checking the insertion result.

```python
if prepared_data:
result = collection.insert_many(prepared_data)
print(f'Inserted {len(result.inserted_ids)} documents into MongoDB.')
else:
print('No data to insert.')
```

By following these steps, you can efficiently move data from Google Directory to a MongoDB database without relying on third-party connectors or integrations.