googleapis_auth/lib/auth_io.dart - third_party/dart-pkg - Git at Google

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 library googleapis_auth.auth_io;

 import 'dart:io';

 import 'package:http/http.dart';

 import 'auth.dart';
 import 'src/auth_http_utils.dart';
 import 'src/adc_utils.dart';
 import 'src/http_client_base.dart';
 import 'src/oauth2_flows/auth_code.dart';
 import 'src/oauth2_flows/jwt.dart';
 import 'src/oauth2_flows/metadata_server.dart';
 import 'src/typedefs.dart';

 export 'auth.dart';
 export 'src/typedefs.dart';

 /// Create a client using [Application Default Credentials][ADC].
 ///
 /// Looks for credentials in the following order of preference:
 ///  1. A JSON file whose path is specified by `GOOGLE_APPLICATION_CREDENTIALS`,
 ///     this file typically contains [exported service account keys][svc-keys].
 ///  2. A JSON file created by [`gcloud auth application-default login`][gcloud-login]
 ///     in a well-known location (`%APPDATA%/gcloud/application_default_credentials.json`
 ///     on Windows and `$HOME/.config/gcloud/application_default_credentials.json` on Linux/Mac).
 ///  3. On Google Compute Engine and App Engine Flex we fetch credentials from
 ///     [GCE metadata service][metadata].
 ///
 /// [metadata]: https://cloud.google.com/compute/docs/storing-retrieving-metadata
 /// [svc-keys]: https://cloud.google.com/docs/authentication/getting-started
 /// [gcloud-login]: https://cloud.google.com/sdk/gcloud/reference/auth/application-default/login
 /// [ADC]: https://cloud.google.com/docs/authentication/production
 Future<AutoRefreshingAuthClient> clientViaApplicationDefaultCredentials({
   List<String> scopes,
   Client baseClient,
 }) async {
   if (baseClient == null) {
     baseClient = new Client();
   } else {
     baseClient = nonClosingClient(baseClient);
   }

   // If env var specifies a file to load credentials from we'll do that.
   final credsEnv = Platform.environment['GOOGLE_APPLICATION_CREDENTIALS'];
   if (credsEnv != null && credsEnv.isNotEmpty) {
     // If env var is specific and not empty, we always try to load, even if
     // the file doesn't exist.
     return await fromApplicationsCredentialsFile(
       File(credsEnv),
       'GOOGLE_APPLICATION_CREDENTIALS',
       scopes,
       baseClient,
     );
   }

   // Attempt to use file created by `gcloud auth application-default login`
   File credFile;
   if (Platform.isWindows) {
     credFile = File.fromUri(Uri.directory(Platform.environment['APPDATA'])
         .resolve('gcloud/application_default_credentials.json'));
   } else {
     credFile = File.fromUri(Uri.directory(Platform.environment['HOME'])
         .resolve('.config/gcloud/application_default_credentials.json'));
   }
   // Only try to load from credFile if it exists.
   if (await credFile.exists()) {
     return await fromApplicationsCredentialsFile(
       credFile,
       '`gcloud auth application-default login`',
       scopes,
       baseClient,
     );
   }

   return await clientViaMetadataServer(baseClient: baseClient);
 }

 /// Obtains oauth2 credentials and returns an authenticated HTTP client.
 ///
 /// See [obtainAccessCredentialsViaUserConsent] for specifics about the
 /// arguments used for obtaining access credentials.
 ///
 /// Once access credentials have been obtained, this function will complete
 /// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
 /// it will use it's refresh token (if available) to obtain new credentials.
 /// See [autoRefreshingClient] for more information.
 ///
 /// If [baseClient] is not given, one will be automatically created. It will be
 /// used for making authenticated HTTP requests.
 ///
 /// The user is responsible for closing the returned HTTP [Client].
 /// Closing the returned [Client] will not close [baseClient].
 Future<AutoRefreshingAuthClient> clientViaUserConsent(
     ClientId clientId, List<String> scopes, PromptUserForConsent userPrompt,
     {Client baseClient}) async {
   bool closeUnderlyingClient = false;
   if (baseClient == null) {
     baseClient = new Client();
     closeUnderlyingClient = true;
   }

   var flow = new AuthorizationCodeGrantServerFlow(
       clientId, scopes, baseClient, userPrompt);

   AccessCredentials credentials;

   try {
     credentials = await flow.run();
   } catch (e) {
     if (closeUnderlyingClient) {
       baseClient.close();
     }
     rethrow;
   }
   return new AutoRefreshingClient(baseClient, clientId, credentials,
       closeUnderlyingClient: closeUnderlyingClient);
 }

 /// Obtains oauth2 credentials and returns an authenticated HTTP client.
 ///
 /// See [obtainAccessCredentialsViaUserConsentManual] for specifics about the
 /// arguments used for obtaining access credentials.
 ///
 /// Once access credentials have been obtained, this function will complete
 /// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
 /// it will use it's refresh token (if available) to obtain new credentials.
 /// See [autoRefreshingClient] for more information.
 ///
 /// If [baseClient] is not given, one will be automatically created. It will be
 /// used for making authenticated HTTP requests.
 ///
 /// The user is responsible for closing the returned HTTP [Client].
 /// Closing the returned [Client] will not close [baseClient].
 Future<AutoRefreshingAuthClient> clientViaUserConsentManual(ClientId clientId,
     List<String> scopes, PromptUserForConsentManual userPrompt,
     {Client baseClient}) async {
   bool closeUnderlyingClient = false;
   if (baseClient == null) {
     baseClient = new Client();
     closeUnderlyingClient = true;
   }

   var flow = new AuthorizationCodeGrantManualFlow(
       clientId, scopes, baseClient, userPrompt);

   AccessCredentials credentials;

   try {
     credentials = await flow.run();
   } catch (e) {
     if (closeUnderlyingClient) {
       baseClient.close();
     }
     rethrow;
   }

   return new AutoRefreshingClient(baseClient, clientId, credentials,
       closeUnderlyingClient: closeUnderlyingClient);
 }

 /// Obtains oauth2 credentials and returns an authenticated HTTP client.
 ///
 /// See [obtainAccessCredentialsViaServiceAccount] for specifics about the
 /// arguments used for obtaining access credentials.
 ///
 /// Once access credentials have been obtained, this function will complete
 /// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
 /// it will obtain new access credentials.
 ///
 /// If [baseClient] is not given, one will be automatically created. It will be
 /// used for making authenticated HTTP requests and for obtaining access
 /// credentials.
 ///
 /// The user is responsible for closing the returned HTTP [Client].
 /// Closing the returned [Client] will not close [baseClient].
 Future<AutoRefreshingAuthClient> clientViaServiceAccount(
     ServiceAccountCredentials clientCredentials, List<String> scopes,
     {Client baseClient}) async {
   if (baseClient == null) {
     baseClient = new Client();
   } else {
     baseClient = nonClosingClient(baseClient);
   }

   var flow = new JwtFlow(
       clientCredentials.email,
       clientCredentials.privateRSAKey,
       clientCredentials.impersonatedUser,
       scopes,
       baseClient);

   AccessCredentials credentials;
   try {
     credentials = await flow.run();
   } catch (e) {
     baseClient.close();
     rethrow;
   }

   return new _ServiceAccountClient(baseClient, credentials, flow);
 }

 /// Obtains oauth2 credentials and returns an authenticated HTTP client.
 ///
 /// See [obtainAccessCredentialsViaMetadataServer] for specifics about the
 /// arguments used for obtaining access credentials.
 ///
 /// Once access credentials have been obtained, this function will complete
 /// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
 /// it will obtain new access credentials.
 ///
 /// If [baseClient] is not given, one will be automatically created. It will be
 /// used for making authenticated HTTP requests and for obtaining access
 /// credentials.
 ///
 /// The user is responsible for closing the returned HTTP [Client].
 /// Closing the returned [Client] will not close [baseClient].
 Future<AutoRefreshingAuthClient> clientViaMetadataServer(
     {Client baseClient}) async {
   if (baseClient == null) {
     baseClient = new Client();
   } else {
     baseClient = nonClosingClient(baseClient);
   }

   var flow = new MetadataServerAuthorizationFlow(baseClient);

   AccessCredentials credentials;

   try {
     credentials = await flow.run();
   } catch (e) {
     baseClient.close();
     rethrow;
   }
   return new _MetadataServerClient(baseClient, credentials, flow);
 }

 /// Obtains a HTTP client which uses the given [apiKey] for making HTTP
 /// requests.
 ///
 /// Note that the returned client should *only* be used for making HTTP requests
 /// to Google Services. The [apiKey] should not be disclosed to third parties.
 ///
 /// The user is responsible for closing the returned HTTP [Client].
 /// Closing the returned [Client] will not close [baseClient].
 Client clientViaApiKey(String apiKey, {Client baseClient}) {
   if (baseClient == null) {
     baseClient = new Client();
   } else {
     baseClient = nonClosingClient(baseClient);
   }
   return new ApiKeyClient(baseClient, apiKey);
 }

 /// Obtain oauth2 [AccessCredentials] using the oauth2 authentication code flow.
 ///
 /// The returned future will complete with `AccessCredentials` if the user
 /// has given the application access to it's data. Otherwise the future will
 /// complete with a `UserConsentException`.
 ///
 /// In case another error occurs the returned future will complete with an
 /// `Exception`.
 ///
 /// [userPrompt] will be used for directing the user/user-agent to a URI. See
 /// [PromptUserForConsent] for more information.
 ///
 /// [client] will be used for obtaining `AccessCredentials` from an
 /// authorization code.
 ///
 /// The [ClientId] can be obtained in the Google Cloud Console.
 Future<AccessCredentials> obtainAccessCredentialsViaUserConsent(
     ClientId clientId,
     List<String> scopes,
     Client client,
     PromptUserForConsent userPrompt) {
   return new AuthorizationCodeGrantServerFlow(
           clientId, scopes, client, userPrompt)
       .run();
 }

 /// Obtain oauth2 [AccessCredentials] using the oauth2 authentication code flow.
 ///
 /// The returned future will complete with `AccessCredentials` if the user
 /// has given the application access to it's data. Otherwise the future will
 /// complete with a `UserConsentException`.
 ///
 /// In case another error occurs the returned future will complete with an
 /// `Exception`.
 ///
 /// [userPrompt] will be used for directing the user/user-agent to a URI. See
 /// [PromptUserForConsentManual] for more information.
 ///
 /// [client] will be used for obtaining `AccessCredentials` from an
 /// authorization code.
 ///
 /// The [ClientId] can be obtained in the Google Cloud Console.
 Future<AccessCredentials> obtainAccessCredentialsViaUserConsentManual(
     ClientId clientId,
     List<String> scopes,
     Client client,
     PromptUserForConsentManual userPrompt) {
   return new AuthorizationCodeGrantManualFlow(
           clientId, scopes, client, userPrompt)
       .run();
 }

 /// Obtain oauth2 [AccessCredentials] using service account credentials.
 ///
 /// In case the service account has no access to the requested scopes or another
 /// error occurs the returned future will complete with an `Exception`.
 ///
 /// [baseClient] will be used for obtaining `AccessCredentials`.
 ///
 /// The [ServiceAccountCredentials] can be obtained in the Google Cloud Console.
 Future<AccessCredentials> obtainAccessCredentialsViaServiceAccount(
     ServiceAccountCredentials clientCredentials,
     List<String> scopes,
     Client baseClient) {
   return new JwtFlow(clientCredentials.email, clientCredentials.privateRSAKey,
           clientCredentials.impersonatedUser, scopes, baseClient)
       .run();
 }

 /// Obtain oauth2 [AccessCredentials] using the metadata API on ComputeEngine.
 ///
 /// In case the VM was not configured with access to the requested scopes or an
 /// error occurs the returned future will complete with an `Exception`.
 ///
 /// [baseClient] will be used for obtaining `AccessCredentials`.
 ///
 /// No credentials are needed. But this function is only intended to work on a
 /// Google Compute Engine VM with configured access to Google APIs.
 Future<AccessCredentials> obtainAccessCredentialsViaMetadataServer(
     Client baseClient) {
   return new MetadataServerAuthorizationFlow(baseClient).run();
 }

 /// Obtain oauth2 [AccessCredentials] by exchanging an authorization code.
 ///
 /// Running a hybrid oauth2 flow as described in the
 /// `googleapis_auth.auth_browser` library results in a `HybridFlowResult` which
 /// contains short-lived [AccessCredentials] for the client and an authorization
 /// code. This authorization code needs to be transferred to the server, which
 /// can exchange it against long-lived [AccessCredentials].
 ///
 /// If the authorization code was obtained using the mentioned hybrid flow, the
 /// [redirectUrl] must be `"postmessage"` (default).
 ///
 /// If you obtained the authorization code using a different mechanism, the
 /// [redirectUrl] must be the same that was used to obtain the code.
 ///
 /// NOTE: Only the server application will know the `client secret` - which is
 /// necessary to exchange an authorization code against access tokens.
 ///
 /// NOTE: It is important to transmit the authorization code in a secure manner
 /// to the server. You should use "anti-request forgery state tokens" to guard
 /// against "cross site request forgery" attacks.
 /// An example on how to do this can be found here:
 ///   https://developers.google.com/+/web/signin/server-side-flow
 Future<AccessCredentials> obtainAccessCredentialsViaCodeExchange(
     Client baseClient, ClientId clientId, String code,
     {String redirectUrl: 'postmessage'}) {
   return obtainAccessCredentialsUsingCode(
       clientId, code, redirectUrl, baseClient);
 }

 /// Will close the underlying `http.Client`.
 class _ServiceAccountClient extends AutoRefreshDelegatingClient {
   final JwtFlow flow;
   AccessCredentials credentials;
   Client authClient;

   _ServiceAccountClient(Client client, this.credentials, this.flow)
       : super(client) {
     authClient = authenticatedClient(baseClient, credentials);
   }

   Future<StreamedResponse> send(BaseRequest request) async {
     if (!credentials.accessToken.hasExpired) {
       return authClient.send(request);
     } else {
       var newCredentials = await flow.run();
       notifyAboutNewCredentials(newCredentials);
       credentials = newCredentials;
       authClient = authenticatedClient(baseClient, credentials);
       return authClient.send(request);
     }
   }
 }

 /// Will close the underlying `http.Client`.
 class _MetadataServerClient extends AutoRefreshDelegatingClient {
   final MetadataServerAuthorizationFlow flow;
   AccessCredentials credentials;
   Client authClient;

   _MetadataServerClient(Client client, this.credentials, this.flow)
       : super(client) {
     authClient = authenticatedClient(baseClient, credentials);
   }

   Future<StreamedResponse> send(BaseRequest request) async {
     if (!credentials.accessToken.hasExpired) {
       return authClient.send(request);
     }

     var newCredentials = await flow.run();
     notifyAboutNewCredentials(newCredentials);
     credentials = newCredentials;
     authClient = authenticatedClient(baseClient, credentials);
     return authClient.send(request);
   }
 }
	// Copyright (c) 2014, the Dart project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	library googleapis_auth.auth_io;

	import 'dart:io';

	import 'package:http/http.dart';

	import 'auth.dart';
	import 'src/auth_http_utils.dart';
	import 'src/adc_utils.dart';
	import 'src/http_client_base.dart';
	import 'src/oauth2_flows/auth_code.dart';
	import 'src/oauth2_flows/jwt.dart';
	import 'src/oauth2_flows/metadata_server.dart';
	import 'src/typedefs.dart';

	export 'auth.dart';
	export 'src/typedefs.dart';

	/// Create a client using [Application Default Credentials][ADC].
	///
	/// Looks for credentials in the following order of preference:
	/// 1. A JSON file whose path is specified by `GOOGLE_APPLICATION_CREDENTIALS`,
	/// this file typically contains [exported service account keys][svc-keys].
	/// 2. A JSON file created by [`gcloud auth application-default login`][gcloud-login]
	/// in a well-known location (`%APPDATA%/gcloud/application_default_credentials.json`
	/// on Windows and `$HOME/.config/gcloud/application_default_credentials.json` on Linux/Mac).
	/// 3. On Google Compute Engine and App Engine Flex we fetch credentials from
	/// [GCE metadata service][metadata].
	///
	/// [metadata]: https://cloud.google.com/compute/docs/storing-retrieving-metadata
	/// [svc-keys]: https://cloud.google.com/docs/authentication/getting-started
	/// [gcloud-login]: https://cloud.google.com/sdk/gcloud/reference/auth/application-default/login
	/// [ADC]: https://cloud.google.com/docs/authentication/production
	Future<AutoRefreshingAuthClient> clientViaApplicationDefaultCredentials({
	List<String> scopes,
	Client baseClient,
	}) async {
	if (baseClient == null) {
	baseClient = new Client();
	} else {
	baseClient = nonClosingClient(baseClient);
	}

	// If env var specifies a file to load credentials from we'll do that.
	final credsEnv = Platform.environment['GOOGLE_APPLICATION_CREDENTIALS'];
	if (credsEnv != null && credsEnv.isNotEmpty) {
	// If env var is specific and not empty, we always try to load, even if
	// the file doesn't exist.
	return await fromApplicationsCredentialsFile(
	File(credsEnv),
	'GOOGLE_APPLICATION_CREDENTIALS',
	scopes,
	baseClient,
	);
	}

	// Attempt to use file created by `gcloud auth application-default login`
	File credFile;
	if (Platform.isWindows) {
	credFile = File.fromUri(Uri.directory(Platform.environment['APPDATA'])
	.resolve('gcloud/application_default_credentials.json'));
	} else {
	credFile = File.fromUri(Uri.directory(Platform.environment['HOME'])
	.resolve('.config/gcloud/application_default_credentials.json'));
	}
	// Only try to load from credFile if it exists.
	if (await credFile.exists()) {
	return await fromApplicationsCredentialsFile(
	credFile,
	'`gcloud auth application-default login`',
	scopes,
	baseClient,
	);
	}

	return await clientViaMetadataServer(baseClient: baseClient);
	}

	/// Obtains oauth2 credentials and returns an authenticated HTTP client.
	///
	/// See [obtainAccessCredentialsViaUserConsent] for specifics about the
	/// arguments used for obtaining access credentials.
	///
	/// Once access credentials have been obtained, this function will complete
	/// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
	/// it will use it's refresh token (if available) to obtain new credentials.
	/// See [autoRefreshingClient] for more information.
	///
	/// If [baseClient] is not given, one will be automatically created. It will be
	/// used for making authenticated HTTP requests.
	///
	/// The user is responsible for closing the returned HTTP [Client].
	/// Closing the returned [Client] will not close [baseClient].
	Future<AutoRefreshingAuthClient> clientViaUserConsent(
	ClientId clientId, List<String> scopes, PromptUserForConsent userPrompt,
	{Client baseClient}) async {
	bool closeUnderlyingClient = false;
	if (baseClient == null) {
	baseClient = new Client();
	closeUnderlyingClient = true;
	}

	var flow = new AuthorizationCodeGrantServerFlow(
	clientId, scopes, baseClient, userPrompt);

	AccessCredentials credentials;

	try {
	credentials = await flow.run();
	} catch (e) {
	if (closeUnderlyingClient) {
	baseClient.close();
	}
	rethrow;
	}
	return new AutoRefreshingClient(baseClient, clientId, credentials,
	closeUnderlyingClient: closeUnderlyingClient);
	}

	/// Obtains oauth2 credentials and returns an authenticated HTTP client.
	///
	/// See [obtainAccessCredentialsViaUserConsentManual] for specifics about the
	/// arguments used for obtaining access credentials.
	///
	/// Once access credentials have been obtained, this function will complete
	/// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
	/// it will use it's refresh token (if available) to obtain new credentials.
	/// See [autoRefreshingClient] for more information.
	///
	/// If [baseClient] is not given, one will be automatically created. It will be
	/// used for making authenticated HTTP requests.
	///
	/// The user is responsible for closing the returned HTTP [Client].
	/// Closing the returned [Client] will not close [baseClient].
	Future<AutoRefreshingAuthClient> clientViaUserConsentManual(ClientId clientId,
	List<String> scopes, PromptUserForConsentManual userPrompt,
	{Client baseClient}) async {
	bool closeUnderlyingClient = false;
	if (baseClient == null) {
	baseClient = new Client();
	closeUnderlyingClient = true;
	}

	var flow = new AuthorizationCodeGrantManualFlow(
	clientId, scopes, baseClient, userPrompt);

	AccessCredentials credentials;

	try {
	credentials = await flow.run();
	} catch (e) {
	if (closeUnderlyingClient) {
	baseClient.close();
	}
	rethrow;
	}

	return new AutoRefreshingClient(baseClient, clientId, credentials,
	closeUnderlyingClient: closeUnderlyingClient);
	}

	/// Obtains oauth2 credentials and returns an authenticated HTTP client.
	///
	/// See [obtainAccessCredentialsViaServiceAccount] for specifics about the
	/// arguments used for obtaining access credentials.
	///
	/// Once access credentials have been obtained, this function will complete
	/// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
	/// it will obtain new access credentials.
	///
	/// If [baseClient] is not given, one will be automatically created. It will be
	/// used for making authenticated HTTP requests and for obtaining access
	/// credentials.
	///
	/// The user is responsible for closing the returned HTTP [Client].
	/// Closing the returned [Client] will not close [baseClient].
	Future<AutoRefreshingAuthClient> clientViaServiceAccount(
	ServiceAccountCredentials clientCredentials, List<String> scopes,
	{Client baseClient}) async {
	if (baseClient == null) {
	baseClient = new Client();
	} else {
	baseClient = nonClosingClient(baseClient);
	}

	var flow = new JwtFlow(
	clientCredentials.email,
	clientCredentials.privateRSAKey,
	clientCredentials.impersonatedUser,
	scopes,
	baseClient);

	AccessCredentials credentials;
	try {
	credentials = await flow.run();
	} catch (e) {
	baseClient.close();
	rethrow;
	}

	return new _ServiceAccountClient(baseClient, credentials, flow);
	}

	/// Obtains oauth2 credentials and returns an authenticated HTTP client.
	///
	/// See [obtainAccessCredentialsViaMetadataServer] for specifics about the
	/// arguments used for obtaining access credentials.
	///
	/// Once access credentials have been obtained, this function will complete
	/// with an auto-refreshing HTTP client. Once the `AccessCredentials` expire
	/// it will obtain new access credentials.
	///
	/// If [baseClient] is not given, one will be automatically created. It will be
	/// used for making authenticated HTTP requests and for obtaining access
	/// credentials.
	///
	/// The user is responsible for closing the returned HTTP [Client].
	/// Closing the returned [Client] will not close [baseClient].
	Future<AutoRefreshingAuthClient> clientViaMetadataServer(
	{Client baseClient}) async {
	if (baseClient == null) {
	baseClient = new Client();
	} else {
	baseClient = nonClosingClient(baseClient);
	}

	var flow = new MetadataServerAuthorizationFlow(baseClient);

	AccessCredentials credentials;

	try {
	credentials = await flow.run();
	} catch (e) {
	baseClient.close();
	rethrow;
	}
	return new _MetadataServerClient(baseClient, credentials, flow);
	}

	/// Obtains a HTTP client which uses the given [apiKey] for making HTTP
	/// requests.
	///
	/// Note that the returned client should only be used for making HTTP requests
	/// to Google Services. The [apiKey] should not be disclosed to third parties.
	///
	/// The user is responsible for closing the returned HTTP [Client].
	/// Closing the returned [Client] will not close [baseClient].
	Client clientViaApiKey(String apiKey, {Client baseClient}) {
	if (baseClient == null) {
	baseClient = new Client();
	} else {
	baseClient = nonClosingClient(baseClient);
	}
	return new ApiKeyClient(baseClient, apiKey);
	}

	/// Obtain oauth2 [AccessCredentials] using the oauth2 authentication code flow.
	///
	/// The returned future will complete with `AccessCredentials` if the user
	/// has given the application access to it's data. Otherwise the future will
	/// complete with a `UserConsentException`.
	///
	/// In case another error occurs the returned future will complete with an
	/// `Exception`.
	///
	/// [userPrompt] will be used for directing the user/user-agent to a URI. See
	/// [PromptUserForConsent] for more information.
	///
	/// [client] will be used for obtaining `AccessCredentials` from an
	/// authorization code.
	///
	/// The [ClientId] can be obtained in the Google Cloud Console.
	Future<AccessCredentials> obtainAccessCredentialsViaUserConsent(
	ClientId clientId,
	List<String> scopes,
	Client client,
	PromptUserForConsent userPrompt) {
	return new AuthorizationCodeGrantServerFlow(
	clientId, scopes, client, userPrompt)
	.run();
	}

	/// Obtain oauth2 [AccessCredentials] using the oauth2 authentication code flow.
	///
	/// The returned future will complete with `AccessCredentials` if the user
	/// has given the application access to it's data. Otherwise the future will
	/// complete with a `UserConsentException`.
	///
	/// In case another error occurs the returned future will complete with an
	/// `Exception`.
	///
	/// [userPrompt] will be used for directing the user/user-agent to a URI. See
	/// [PromptUserForConsentManual] for more information.
	///
	/// [client] will be used for obtaining `AccessCredentials` from an
	/// authorization code.
	///
	/// The [ClientId] can be obtained in the Google Cloud Console.
	Future<AccessCredentials> obtainAccessCredentialsViaUserConsentManual(
	ClientId clientId,
	List<String> scopes,
	Client client,
	PromptUserForConsentManual userPrompt) {
	return new AuthorizationCodeGrantManualFlow(
	clientId, scopes, client, userPrompt)
	.run();
	}

	/// Obtain oauth2 [AccessCredentials] using service account credentials.
	///
	/// In case the service account has no access to the requested scopes or another
	/// error occurs the returned future will complete with an `Exception`.
	///
	/// [baseClient] will be used for obtaining `AccessCredentials`.
	///
	/// The [ServiceAccountCredentials] can be obtained in the Google Cloud Console.
	Future<AccessCredentials> obtainAccessCredentialsViaServiceAccount(
	ServiceAccountCredentials clientCredentials,
	List<String> scopes,
	Client baseClient) {
	return new JwtFlow(clientCredentials.email, clientCredentials.privateRSAKey,
	clientCredentials.impersonatedUser, scopes, baseClient)
	.run();
	}

	/// Obtain oauth2 [AccessCredentials] using the metadata API on ComputeEngine.
	///
	/// In case the VM was not configured with access to the requested scopes or an
	/// error occurs the returned future will complete with an `Exception`.
	///
	/// [baseClient] will be used for obtaining `AccessCredentials`.
	///
	/// No credentials are needed. But this function is only intended to work on a
	/// Google Compute Engine VM with configured access to Google APIs.
	Future<AccessCredentials> obtainAccessCredentialsViaMetadataServer(
	Client baseClient) {
	return new MetadataServerAuthorizationFlow(baseClient).run();
	}

	/// Obtain oauth2 [AccessCredentials] by exchanging an authorization code.
	///
	/// Running a hybrid oauth2 flow as described in the
	/// `googleapis_auth.auth_browser` library results in a `HybridFlowResult` which
	/// contains short-lived [AccessCredentials] for the client and an authorization
	/// code. This authorization code needs to be transferred to the server, which
	/// can exchange it against long-lived [AccessCredentials].
	///
	/// If the authorization code was obtained using the mentioned hybrid flow, the
	/// [redirectUrl] must be `"postmessage"` (default).
	///
	/// If you obtained the authorization code using a different mechanism, the
	/// [redirectUrl] must be the same that was used to obtain the code.
	///
	/// NOTE: Only the server application will know the `client secret` - which is
	/// necessary to exchange an authorization code against access tokens.
	///
	/// NOTE: It is important to transmit the authorization code in a secure manner
	/// to the server. You should use "anti-request forgery state tokens" to guard
	/// against "cross site request forgery" attacks.
	/// An example on how to do this can be found here:
	/// https://developers.google.com/+/web/signin/server-side-flow
	Future<AccessCredentials> obtainAccessCredentialsViaCodeExchange(
	Client baseClient, ClientId clientId, String code,
	{String redirectUrl: 'postmessage'}) {
	return obtainAccessCredentialsUsingCode(
	clientId, code, redirectUrl, baseClient);
	}

	/// Will close the underlying `http.Client`.
	class _ServiceAccountClient extends AutoRefreshDelegatingClient {
	final JwtFlow flow;
	AccessCredentials credentials;
	Client authClient;

	_ServiceAccountClient(Client client, this.credentials, this.flow)
	: super(client) {
	authClient = authenticatedClient(baseClient, credentials);
	}

	Future<StreamedResponse> send(BaseRequest request) async {
	if (!credentials.accessToken.hasExpired) {
	return authClient.send(request);
	} else {
	var newCredentials = await flow.run();
	notifyAboutNewCredentials(newCredentials);
	credentials = newCredentials;
	authClient = authenticatedClient(baseClient, credentials);
	return authClient.send(request);
	}
	}
	}

	/// Will close the underlying `http.Client`.
	class _MetadataServerClient extends AutoRefreshDelegatingClient {
	final MetadataServerAuthorizationFlow flow;
	AccessCredentials credentials;
	Client authClient;

	_MetadataServerClient(Client client, this.credentials, this.flow)
	: super(client) {
	authClient = authenticatedClient(baseClient, credentials);
	}

	Future<StreamedResponse> send(BaseRequest request) async {
	if (!credentials.accessToken.hasExpired) {
	return authClient.send(request);
	}

	var newCredentials = await flow.run();
	notifyAboutNewCredentials(newCredentials);
	credentials = newCredentials;
	authClient = authenticatedClient(baseClient, credentials);
	return authClient.send(request);
	}
	}