### Import Google API Libraries in Dart

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Import the authentication and Drive API libraries into your Dart file. This example uses 'auth_browser' for browser-based authentication and 'drive/v2' for the Drive API.

```dart
import 'package:googleapis_auth/auth_browser.dart' as auth;
import 'package:googleapis/drive/v2.dart' as drive;
```

--------------------------------

### Obtain Authenticated Client via Metadata Server

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Get an authenticated and auto-refreshing HTTP client using the metadata service. Remember to close the client when finished.

```dart
import 'package:googleapis_auth/auth_io.dart';

// Use the metadata service to get an authenticated and auto refreshing client.
Future<AuthClient> obtainAuthenticatedClient() async {
  final AuthClient client = await clientViaMetadataServer();

  return client; // Remember to close the client when you are finished with it.
}
```

--------------------------------

### Implement Browser OAuth 2.0 Flow

Source: https://github.com/google/googleapis.dart/blob/master/README.md

This function manages the implicit browser flow for OAuth 2.0. It first attempts to get a client without forcing user consent. If consent is required or denied, it prompts the user via a button click.

```dart
Future authorizedClient(ButtonElement loginButton, auth.ClientId id, scopes) {
  return auth.createImplicitBrowserFlow(id, scopes)
      .then((auth.BrowserOAuth2Flow flow) {
        return flow.clientViaUserConsent(forceUserConsent: false).catchError((_) {
          loginButton.text = '';
          return loginButton.onClick.first.then((_) {
            return flow.clientViaUserConsent(forceUserConsent: true);
          });
        }, test: (error) => error is auth.UserConsentException);
  });
}
```

--------------------------------

### Obtain Authenticated Client via Service Account

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Get an authenticated and auto-refreshing HTTP client using service account credentials. This client is suitable for autonomous applications accessing Google Cloud Project data. Remember to close the client when finished.

```dart
import 'package:googleapis_auth/auth_io.dart';

// Use service account credentials to get an authenticated and auto refreshing
// client.
Future<AuthClient> obtainAuthenticatedClient() async {
  final accountCredentials = ServiceAccountCredentials.fromJson({
    'private_key_id': '<please fill in>',
    'private_key': '<please fill in>',
    'client_email': '<please fill in>@developer.gserviceaccount.com',
    'client_id': '<please fill in>.apps.googleusercontent.com',
    'type': 'service_account'
  });
  final scopes = ['scope1'];

  final AuthClient client =
  await clientViaServiceAccount(accountCredentials, scopes);

  return client; // Remember to close the client when you are finished with it.
}
```

--------------------------------

### Display Help for Discovery Generator

Source: https://github.com/google/googleapis.dart/blob/master/discoveryapis_generator/README.md

Run the generator with the -h flag to see all available commands and options.

```bash
dart bin/generate.dart -h
```

--------------------------------

### Rungoogleapis_auth Package Tests

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Execute tests for the `googleapis_auth` package. This includes fetching dependencies, running tests, and formatting the code.

```console
$ pushd googleapis_auth
$ pub get
$ pub run test
$ dart format . --fix
$ popd
```

--------------------------------

### Generate APIs

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Generate API client libraries using the `generate.dart` script with the `run_config generate` command. This step should be performed after downloading discovery documents.

```console
$ dart generator/bin/generate.dart run_config generate
```

--------------------------------

### Download APIs using config.yaml

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Download API discovery documents using the `generate.dart` script with the `run_config download` command. It's recommended to use Cloud Shell for this operation, especially on corporate networks.

```console
$ dart generator/bin/generate.dart run_config download
```

--------------------------------

### Run Generatedgoogleapis Tests

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Execute tests for the generated Google APIs packages (`googleapis` and `googleapis_beta`). This involves navigating to the respective directories, fetching dependencies, and running the tests.

```console
$ pushd generated/googleapis
$ pub get
$ pub run test
$ cd ../googleapis_beta
$ pub get
$ pub run test
$ popd
```

--------------------------------

### Generate API Package from Discovery Documents

Source: https://github.com/google/googleapis.dart/blob/master/discoveryapis_generator/README.md

Use the 'package' subcommand to create a new Dart API client library package. Specify input and output directories, along with package metadata.

```bash
dart bin/generate.dart package -i <input-dir> -o <output-dir> --package-name <package-name> --package-version <package-version> --package-description <package-description> --package-author <package-author> --package-repository <package-repository>
```

--------------------------------

### Initialize Storage API Client

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Define the necessary scopes for your API operations and obtain an authenticated HTTP client using your service account credentials. This client is then used to instantiate the Storage API.

```dart
final scopes = [storage.StorageApi.DevstorageFullControlScope];
... 
var api = new storage.StorageApi(client);
```

--------------------------------

### Create Service Account Credentials from JSON

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Instantiate service account credentials using a JSON string. Ensure you replace the placeholder values with your actual service account details obtained from the Cloud Console.

```dart
final accountCredentials = new auth.ServiceAccountCredentials.fromJson(r'''
{
  "private_key_id": "<please fill in>",
  "private_key": "<please fill in>",
  "client_email": "<please fill in>@developer.gserviceaccount.com",
  "client_id": "<please fill in>.apps.googleusercontent.com",
  "type": "service_account"
}''');
```

--------------------------------

### Obtain Credentials via Metadata Server

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Use the metadata service to obtain OAuth credentials on a Compute Engine VM. Ensure the http client is closed after use.

```dart
import 'package:googleapis_auth/auth_io.dart';
import 'package:http/http.dart' as http;

// Use the metadata service to obtain oauth credentials.
Future<AccessCredentials> obtainCredentials() async {
  final client = http.Client();

  final credentials =
  await obtainAccessCredentialsViaMetadataServer(client);

  client.close();
  return credentials;
}
```

--------------------------------

### Create Drive API Instance

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Instantiate the DriveApi object by passing the authenticated HTTP client. This object provides methods to interact with the Google Drive API.

```dart
var api = new drive.DriveApi(client);
```

--------------------------------

### Declare Dependencies in pubspec.yaml

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Declare the necessary googleapis_auth and googleapis packages in your pubspec.yaml file to use the Google Drive API and OAuth 2.0.

```yaml
dependencies:
  googleapis_auth: '>=0.1.0 < 0.2.0'
  googleapis: '>=0.1.1 < 0.2.0'
```

--------------------------------

### Upload Media to Google Cloud Storage

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Use the Storage API to upload a media file to a Google Cloud Storage bucket. This involves calling the `insert` method on the `objects` resource of the Storage API.

```dart
return api.objects.insert(null, bucket, name: object, uploadMedia: media);
```

--------------------------------

### Generate API Files into Existing Package

Source: https://github.com/google/googleapis.dart/blob/master/discoveryapis_generator/README.md

Use the 'files' subcommand to generate API files directly into an existing Dart package. This command can also update the pubspec.yaml file.

```bash
dart bin/generate.dart files -i <input-dir> -o <output-dir> -u --core-prefixes
```

--------------------------------

### Authenticate Client with Service Account

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Obtain an authenticated HTTP client by providing the service account credentials and the desired scopes to the `clientViaServiceAccount` function. This client can then be used to interact with Google Cloud APIs.

```dart
auth.clientViaServiceAccount(accountCredentials, scopes).then((client) {
  ...
  var regexp = new RegExp(r'^gs://([^/]+)/(.+)$');
  switch (args.first) {
    case 'upload':
  ...
}
```

--------------------------------

### Obtain Credentials for Client-Side Web App

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Use this for client-side web applications to request access credentials. Requires a Client ID and specified scopes.

```dart
import 'package:googleapis_auth/auth_browser.dart';

// Initialize the browser oauth2 flow functionality then use it to obtain
// credentials.
Future<AccessCredentials> obtainCredentials() => requestAccessCredentials(
      clientId: '....apps.googleusercontent.com',
      scopes: ['scope1', 'scope2'],
    );
```

--------------------------------

### Obtain Authenticated HTTP Client for Client-Side Web App

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Obtain an authenticated HTTP client for client-side web applications. This client will automatically use the obtained credentials for requests. Remember to close the client when finished.

```dart
import 'package:googleapis_auth/auth_browser.dart';
import 'package:http/http.dart' as http;

Future<AuthClient> obtainClient() async {
  final credentials = await requestAccessCredentials(
    clientId: '....apps.googleusercontent.com',
    scopes: ['scope1', 'scope2'],
  );

  return authenticatedClient(http.Client(), credentials);
}
```

--------------------------------

### Initiate Authorized Client Flow

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Call authorizedClient() in your main function to obtain an authenticated HTTP client. This function handles the OAuth 2.0 authorization process, requesting user consent if necessary.

```dart
authorizedClient(loginButton, identifier, scopes).then((client) {
  ...
})
```

--------------------------------

### Access Public Data with API Key

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Obtain an HTTP client that uses an API key for making requests to Google APIs. The API key is used for quota and billing and should not be disclosed.

```dart
import 'package:googleapis_auth/auth_io.dart';

var client = clientViaApiKey('<api-key-from-devconsole>');
// [client] can now be used to make REST calls to Google APIs.

...

client.close();
```

--------------------------------

### Obtain Credentials with Custom Endpoints

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Use custom AuthEndpoints to obtain access credentials via user consent for a non-Google OAuth provider.

```dart
final clientId = ClientId('my-client-id', 'my-client-secret');
final credentials = await obtainAccessCredentialsViaUserConsent(
  clientId,
  ['scope1', 'scope2'],
  client,
  (url) {
    print('Please go to the following URL and grant access:');
    print('  => $url');
    print('');
  },
  authEndpoints: MicrosoftAuthEndpoints(),
);
```

--------------------------------

### Upgrade Dependencies in Generator Directory

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Update project dependencies within the `generator` directory. This involves removing the existing Dart tool cache and running `pub upgrade`.

```console
$ cd generator
$ rm -rf .dart_tool
$ pub upgrade
```

--------------------------------

### Configure Client ID and Scopes

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Define the client ID obtained from the Google Developers Console and the API scopes required for your application. The scope determines the level of access granted to the user's data.

```dart
final identifier = new auth.ClientId(
     "<custom-app-id>.apps.googleusercontent.com",
     null);

final scopes = [drive.DriveApi.DriveScope];
```

--------------------------------

### Search Documents with Google Drive API

Source: https://github.com/google/googleapis.dart/blob/master/README.md

Implement a function to search for documents in Google Drive using the Drive API. This function supports pagination to retrieve all results if the total number exceeds the maximum results per page.

```dart
Future<List<drive.File>> searchTextDocuments(drive.DriveApi api,
                                             int max,
                                             String query) {
  var docs = [];
  Future next(String token) {
    // The API call returns only a subset of the results. It is possible
    // to query through the whole result set via "paging".
    return api.files.list(q: query, pageToken: token, maxResults: max)
        .then((results) {
      docs.addAll(results.items);
      // If we would like to have more documents, we iterate.
      if (docs.length < max && results.nextPageToken != null) {
        return next(results.nextPageToken);
      }
      return docs;
    });
  }
  return next(null);
}
```

--------------------------------

### Obtain Credentials via Service Account

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Use service account credentials to obtain OAuth credentials for autonomous applications. Requires a JSON key file and specified scopes. Ensure the http client is closed after use.

```dart
import 'package:googleapis_auth/auth_io.dart';
import 'package:http/http.dart' as http;

// Use service account credentials to obtain oauth credentials.
Future<AccessCredentials> obtainCredentials() async {
  final accountCredentials = ServiceAccountCredentials.fromJson({
    'private_key_id': '<please fill in>',
    'private_key': '<please fill in>',
    'client_email': '<please fill in>@developer.gserviceaccount.com',
    'client_id': '<please fill in>.apps.googleusercontent.com',
    'type': 'service_account'
  });
  final scopes = ['scope1', 'scope2'];

  final client = http.Client();
  final credentials = await obtainAccessCredentialsViaServiceAccount(
          accountCredentials, scopes, client);

  client.close();
  return credentials;
}
```

--------------------------------

### Define Custom Authentication Endpoints

Source: https://github.com/google/googleapis.dart/blob/master/googleapis_auth/README.md

Subclass AuthEndpoints to provide custom authorization and token URIs for non-Google OAuth providers.

```dart
import 'package:googleapis_auth/auth_io.dart';

class MicrosoftAuthEndpoints extends AuthEndpoints {
  @override
  Uri get authorizationEndpoint =>
      Uri.https('login.microsoftonline.com', 'common/oauth2/v2.0/authorize');

  @override
  Uri get tokenEndpoint =>
      Uri.https('login.microsoftonline.com', 'common/oauth2/v2.0/token');
}
```

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