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Amazon Cognito Identity SDK for Dart

Unofficial Amazon Cognito Identity SDK written in Dart for Dart.

Based on amazon-cognito-identity-js. First version was created by Jonsaw amazon-cognito-identity-dart.

Need ideas to get started?

• Check out use cases below.

• Example Flutter app can be found here.

• Authenticated access to:

  • AppSync + GraphQL found here.
  • API Gateway + Lambda found here.
  • S3 Presigned Post found here.
  • S3 GET Object with Authorization found here.

• Follow the tutorial on Serverless Stack for best Cognito setup.

• Use Custom Storage found here.

• Get AWS credentials with facebook found here.

• Use client secret found here.

• How to use refresh token to keep session valid?

Usage

Use Case 1. Registering a user with the application. One needs to create a CognitoUserPool object by providing a UserPoolId and a ClientId and signing up by using a username, password, attribute list, and validation data.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);
final userAttributes = [
  AttributeArg(name: 'first_name', value: 'Jimmy'),
  AttributeArg(name: 'last_name', value: 'Wong'),
];

var data;
try {
  data = await userPool.signUp(
    '[email protected]',
    'Password001',
     userAttributes: userAttributes,
   );
} catch (e) {
  print(e);
}

Use case 2. Confirming a registered, unauthenticated user using a confirmation code received via SMS/email.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);

final cognitoUser = CognitoUser('[email protected]', userPool);

bool registrationConfirmed = false;
try {
  registrationConfirmed = await cognitoUser.confirmRegistration('123456');
} catch (e) {
  print(e);
}
print(registrationConfirmed);

Use case 3. Resending a confirmation code via SMS/email for confirming registration for unauthenticated users.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);
final cognitoUser = CognitoUser('[email protected]', userPool);
final String status;
try {
  status = await cognitoUser.resendConfirmationCode();
} catch (e) {
  print(e);
}

Use case 4. Authenticating a user and establishing a user session with the Amazon Cognito Identity service.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);
final cognitoUser = CognitoUser('[email protected]', userPool);
final authDetails = AuthenticationDetails(
  username: '[email protected]',
  password: 'Password001',
);
CognitoUserSession session;
try {
  session = await cognitoUser.authenticateUser(authDetails);
} on CognitoUserNewPasswordRequiredException catch (e) {
  // handle New Password challenge
} on CognitoUserMfaRequiredException catch (e) {
  // handle SMS_MFA challenge
} on CognitoUserSelectMfaTypeException catch (e) {
  // handle SELECT_MFA_TYPE challenge
} on CognitoUserMfaSetupException catch (e) {
  // handle MFA_SETUP challenge
} on CognitoUserTotpRequiredException catch (e) {
  // handle SOFTWARE_TOKEN_MFA challenge
} on CognitoUserCustomChallengeException catch (e) {
  // handle CUSTOM_CHALLENGE challenge
} on CognitoUserConfirmationNecessaryException catch (e) {
  // handle User Confirmation Necessary
} on CognitoClientException catch (e) {
  // handle Wrong Username and Password and Cognito Client
}catch (e) {
  print(e);
}
print(session.getAccessToken().getJwtToken());

Use case 5. Retrieve user attributes for authenticated users.

List<CognitoUserAttribute> attributes;
try {
  attributes = await cognitoUser.getUserAttributes();
} catch (e) {
  print(e);
}
attributes.forEach((attribute) {
  print('attribute ${attribute.getName()} has value ${attribute.getValue()}');
});

Use case 6. Verify user attribute for an authenticated user.

var data;
try {
  data = await cognitoUser.getAttributeVerificationCode('email');
} catch {
  print(e);
}
print(data);

// obtain verification code...

bool attributeVerified = false;
try {
  attributeVerified = await cognitoUser.verifyAttribute('email', '123456');
} catch (e) {
  print(e);
}
print(attributeVerified);

Use case 7. Delete user attributes for authenticated users.

try {
  final List<String> attributeList = ['nickname'];
  cognitoUser.deleteAttributes(attributeList);
} catch (e) {
  print(e);
}

Use case 8. Update user attributes for authenticated users.

final List<CognitoUserAttribute> attributes = [];
attributes.add(CognitoUserAttribute(name: 'nickname', value: 'joe'));

try {
  await cognitoUser.updateAttributes(attributes);
} catch (e) {
  print(e);
}

Use case 9. Enabling MFA for a user on a pool that has an optional MFA setting for authenticated users.

bool mfaEnabled = false;
try {
  mfaEnabled = await cognitoUser.enableMfa();
  var mfaOptions = await cognitoManager.cognitoUser.getMFAOptions();
  print('mfaOptions: $mfaOptions');
} catch (e) {
  print(e);
}
print('mfaEnabled: $mfaEnabled');

Use case 10. Disabling MFA for a user on a pool that has an optional MFA setting for authenticated users.

bool mfaDisabled = false;
try {
  mfaDisabled = await cognitoUser.disableMfa();
} catch (e) {
  print(e);
}
print(mfaDisabled);

Use case 11. Changing the current password for authenticated users.

bool passwordChanged = false;
try {
  passwordChanged = await cognitoUser.changePassword(
    'oldPassword',
    'newPassword',
  );
} catch (e) {
  print(e);
}
print(passwordChanged);

Use case 12. Starting and completing a forgot password flow for an unauthenticated user.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);
final cognitoUser = CognitoUser('[email protected]', userPool);

var data;
try {
  data = await cognitoUser.forgotPassword();
} catch (e) {
  print(e);
}
print('Code sent to $data');

// prompt user for verification input...

bool passwordConfirmed = false;
try {
  passwordConfirmed = await cognitoUser.confirmPassword(
      '123456', 'newPassword');
} catch (e) {
  print(e);
}
print(passwordConfirmed);

Use case 13. Deleting authenticated users.

bool userDeleted = false
try {
  userDeleted = await cognitoUser.deleteUser();
} catch (e) {
  print(e);
}
print(userDeleted);

Use case 14. Signing out from the application.

await cognitoUser.signOut();

Use case 15. Global signout for authenticated users (invalidates all issued tokens).

await cognitoUser.globalSignOut();

Use case 16. Manually set key value pairs that can be passed to Cognito Lambda Triggers.

Map<String, String> validationData = {
  'myCustomKey1': 'myCustomValue1',
  'myCustomKey2': 'myCustomValue2',
};

Use case 17. Manually set Authorization header (e.g. JWT token)

signedRequest = SigV4Request(
  awsSigV4Client,
  method: Method.post,
  authorizationHeader: session.idToken.jwtToken, // <---- custom authorizationHeader
  path: '/path',
  headers: Map<String, String>.from({
    CONTENT_TYPE: APPLICATION_GRAPHQL,
    ACCEPT: APPLICATION_JSON,
  }),
  body: Map<String, String>.from(
    {
      QUERY: query,
    },
  ),
);

Use case 18. Resetting an user password after first user authentication (when an account has status FORCE_CHANGE_PASSWORD). When an administrator creates the user pool account then an user has to change its password after first sign-in. Moreover the Cognito User Pool service can send a list of required attributes that user has to set when settings a new password.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx'
);
final cognitoUser = CognitoUser('[email protected]', userPool);
final authDetails = AuthenticationDetails(
  username: '[email protected]',
  password: 'Password001!',
);
CognitoUserSession session;
try {
  session = await cognitoUser.authenticateUser(authDetails);
} on CognitoUserNewPasswordRequiredException catch (e) {
  try {
    if(e.requiredAttributes.isEmpty) {
      // No attribute hast to be set
      session = await cognitoUser.sendNewPasswordRequiredAnswer("NewPassword002!");
    } else {
      // All attributes from the e.requiredAttributes has to be set.
      print(e.requiredAttributes);
      // For example obtain and set the name attribute.
      var attributes = { "name": "Adam Kaminski"};
      session = await cognitoUser.sendNewPasswordRequiredAnswer("NewPassword002!", attributes);
    }
  } on CognitoUserMfaRequiredException catch (e) {
    // handle SMS_MFA challenge
  } on CognitoUserSelectMfaTypeException catch (e) {
    // handle SELECT_MFA_TYPE challenge
  } on CognitoUserMfaSetupException catch (e) {
    // handle MFA_SETUP challenge
  } on CognitoUserTotpRequiredException catch (e) {
    // handle SOFTWARE_TOKEN_MFA challenge
  } on CognitoUserCustomChallengeException catch (e) {
    // handle CUSTOM_CHALLENGE challenge
  } catch (e) {
    print(e);
  }
} on CognitoUserMfaRequiredException catch (e) {
  // handle SMS_MFA challenge
} on CognitoUserSelectMfaTypeException catch (e) {
  // handle SELECT_MFA_TYPE challenge
} on CognitoUserMfaSetupException catch (e) {
  // handle MFA_SETUP challenge
} on CognitoUserTotpRequiredException catch (e) {
  // handle SOFTWARE_TOKEN_MFA challenge
} on CognitoUserCustomChallengeException catch (e) {
  // handle CUSTOM_CHALLENGE challenge
} on CognitoUserConfirmationNecessaryException catch (e) {
  // handle User Confirmation Necessary
} catch (e) {
  print(e);
}
print(session.getAccessToken().getJwtToken());

Use case 19. Using this library with Cognito's federated sign in on mobile devices. Use flutter_webview (https://pub.dev/packages/webview_flutter) to navigate to Cognito's authorize URL. Use flutter_webview's navigationDelegate to catch the redirect to myapp://?code=<AUTH_CODE>. Make a POST request to Cognito's token URL to get your tokens. Create the session and user with the tokens.

  final Completer<WebViewController> _webViewController = Completer<WebViewController>();
  Widget getWebView() {
    var url = "https://${COGNITO_POOL_URL}" +
      ".amazoncognito.com/oauth2/authorize?identity_provider=Google&redirect_uri=" +
      "myapp://&response_type=CODE&client_id=${COGNITO_CLIENT_ID}" +
      "&scope=email%20openid%20profile%20aws.cognito.signin.user.admin";
    return
      WebView(
        initialUrl: url,
        userAgent: 'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) ' +
            'AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Mobile Safari/537.36',
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (WebViewController webViewController) {
          _webViewController.complete(webViewController);
        },
        navigationDelegate: (NavigationRequest request) {
          if (request.url.startsWith("myapp://?code=")) {
            String code = request.url.substring("myapp://?code=".length);
            signUserInWithAuthCode(code);
            return NavigationDecision.prevent;
          }

          return NavigationDecision.navigate;
        },
        gestureNavigationEnabled: true,
      );
  }

  final userPool = CognitoUserPool(
    'ap-southeast-1_xxxxxxxxx',
    'xxxxxxxxxxxxxxxxxxxxxxxxxx'
  );
  static Future signUserInWithAuthCode(String authCode) async {
    String url = "https://${COGNITO_POOL_URL}" +
        ".amazoncognito.com/oauth2/token?grant_type=authorization_code&client_id=" +
        "${COGNITO_CLIENT_ID}&code=" + authCode + "&redirect_uri=myapp://";
    final response = await http.post(url, body: {}, headers: {'Content-Type': 'application/x-www-form-urlencoded'});
    if (response.statusCode != 200) {
      throw Exception("Received bad status code from Cognito for auth code:" +
          response.statusCode.toString() + "; body: " + response.body);
    }

    final tokenData = json.decode(response.body);

    final idToken = CognitoIdToken(tokenData['id_token']);
    final accessToken = CognitoAccessToken(tokenData['access_token']);
    final refreshToken = CognitoRefreshToken(tokenData['refresh_token']);
    final session = CognitoUserSession(idToken, accessToken, refreshToken: refreshToken);
    final user = CognitoUser(null, userPool, signInUserSession: session);

    // NOTE: in order to get the email from the list of user attributes, make sure you select email in the list of
    // attributes in Cognito and map it to the email field in the identity provider.
    final attributes = await user.getUserAttributes();
    for (CognitoUserAttribute attribute in attributes) {
      if (attribute.getName() == "email") {
        user.username = attribute.getValue();
        break;
      }
    }

    return user;
  }
}

Addtional Features

Get AWS Credentials

Get a authenticated user's AWS Credentials. Use with other signing processes like Signature Version 4.

import 'package:amazon_cognito_identity_dart_2/cognito.dart';

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
);
final cognitoUser = CognitoUser('[email protected]', userPool);
final authDetails = AuthenticationDetails(
    username: '[email protected]',
    password: 'Password001',
);
final session = await cognitoUser.authenticateUser(authDetails);

final credentials = CognitoCredentials(
    'ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', userPool);
await credentials.getAwsCredentials(session.getIdToken().getJwtToken());
print(credentials.accessKeyId);
print(credentials.secretAccessKey);
print(credentials.sessionToken);

Signing Requests

For S3 Uploads

S3 Upload to user "folder" using HTTP Presigned Post.

import 'dart:convert';
import 'dart:io';
import 'package:path/path.dart' as path;
import 'package:async/async.dart';
import 'package:http/http.dart' as http;
import 'package:amazon_cognito_identity_dart_2/cognito.dart';
import 'package:amazon_cognito_identity_dart_2/sig_v4.dart';

class Policy {
  String expiration;
  String region;
  String bucket;
  String key;
  String credential;
  String datetime;
  String sessionToken;
  int maxFileSize;

  Policy(
    this.key,
    this.bucket,
    this.datetime,
    this.expiration,
    this.credential,
    this.maxFileSize,
    this.sessionToken,
    {this.region = 'us-east-1'},
   );

  factory Policy.fromS3PresignedPost(
    String key,
    String bucket,
    int expiryMinutes,
    String accessKeyId,
    int maxFileSize,
    String sessionToken,
    {String region},
   ) {
    final datetime = SigV4.generateDatetime();
    final expiration = (DateTime.now())
        .add(Duration(minutes: expiryMinutes))
        .toUtc()
        .toString()
        .split(' ')
        .join('T');
    final cred =
        '$accessKeyId/${SigV4.buildCredentialScope(datetime, region, 's3')}';
    final p = Policy(
        key, bucket, datetime, expiration, cred, maxFileSize, sessionToken,
        region: region);
    return p;
  }

  String encode() {
    final bytes = utf8.encode(toString());
    return base64.encode(bytes);
  }

  @override
  String toString() {
    // Safe to remove the "acl" line if your bucket has no ACL permissions
    return '''
    { "expiration": "${this.expiration}",
      "conditions": [
        {"bucket": "${this.bucket}"},
        ["starts-with", "\$key", "${this.key}"],
        {"acl": "public-read"},
        ["content-length-range", 1, ${this.maxFileSize}],
        {"x-amz-credential": "${this.credential}"},
        {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
        {"x-amz-date": "${this.datetime}" },
        {"x-amz-security-token": "${this.sessionToken}" }
      ]
    }
    ''';
  }
}

void main() async {
  const _awsUserPoolId = 'ap-southeast-xxxxxxxxxxx';
  const _awsClientId = 'xxxxxxxxxxxxxxxxxxxxxxxxxx';

  const _identityPoolId = 'ap-southeast-1:xxxxxxxxx-xxxx-xxxx-xxxxxxxxxxx';
  final _userPool = CognitoUserPool(_awsUserPoolId, _awsClientId);

  final _cognitoUser = CognitoUser('+60100000000', _userPool);
  final authDetails =
      AuthenticationDetails(username: '+60100000000', password: 'p&ssW0RD');

  CognitoUserSession _session;
  try {
    _session = await _cognitoUser.authenticateUser(authDetails);
  } catch (e) {
    print(e);
  }

  final _credentials = CognitoCredentials(_identityPoolId, _userPool);
  await _credentials.getAwsCredentials(_session.getIdToken().getJwtToken());

  const _region = 'ap-southeast-1';
  const _s3Endpoint = 'https://my-s3-bucket.s3-ap-southeast-1.amazonaws.com';

  final file = File(path.join('/path/to/my/folder', 'square-cinnamon.jpg'));

  final stream = http.ByteStream(DelegatingStream.typed(file.openRead()));
  final length = await file.length();

  final uri = Uri.parse(_s3Endpoint);
  final req = http.MultipartRequest("POST", uri);
  final multipartFile = http.MultipartFile('file', stream, length,
      filename: path.basename(file.path));

  final String fileName = 'square-cinnamon.jpg';
  final String usrIdentityId = _credentials.userIdentityId;
  final String bucketKey = 'test/$usrIdentityId/$fileName';

  final policy = Policy.fromS3PresignedPost(
      bucketKey,
      'my-s3-bucket',
      15,
      _credentials.accessKeyId,
      length,
      _credentials.sessionToken,
      region: _region);
  final key = SigV4.calculateSigningKey(
      _credentials.secretAccessKey, policy.datetime, _region, 's3');
  final signature = SigV4.calculateSignature(key, policy.encode());

  req.files.add(multipartFile);
  req.fields['key'] = policy.key;
  req.fields['acl'] = 'public-read'; // Safe to remove this if your bucket has no ACL permissions
  req.fields['X-Amz-Credential'] = policy.credential;
  req.fields['X-Amz-Algorithm'] = 'AWS4-HMAC-SHA256';
  req.fields['X-Amz-Date'] = policy.datetime;
  req.fields['Policy'] = policy.encode();
  req.fields['X-Amz-Signature'] = signature;
  req.fields['x-amz-security-token'] = _credentials.sessionToken;

  try {
    final res = await req.send();
    await for (var value in res.stream.transform(utf8.decoder)) {
      print(value);
    }
  } catch (e) {
    print(e.toString());
  }
}

The role attached to the identity pool (e.g. the ..._poolAuth role) should contain a policy like this:

{
    "Effect": "Allow",
    "Action": [
        "s3:PutObject",
        "s3:GetObject"
    ],
    "Resource": "arn:aws:s3:::BUCKET_NAME/test/${cognito-identity.amazonaws.com:sub}/*"
}

For S3 GET Object

Signing S3 GET Object using Authorization header.

import 'dart:io';
import 'package:path/path.dart' as path;
import 'package:amazon_cognito_identity_dart_2/cognito.dart';
import 'package:amazon_cognito_identity_dart_2/sig_v4.dart';
import 'package:http/http.dart' as http;

void main() {
  const _awsUserPoolId = 'ap-southeast-1_xxxxxxxx';
  const _awsClientId = 'xxxxxxxxxxxxxxxxxxxxxxxxxx';

  const _identityPoolId =
      'ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx';
  final _userPool = CognitoUserPool(_awsUserPoolId, _awsClientId);

  final _cognitoUser = CognitoUser('+60100000000', _userPool);
  final authDetails =
      AuthenticationDetails(username: '+60100000000', password: 'p@ssW0rd');

  CognitoUserSession _session;
  try {
    _session = await _cognitoUser.authenticateUser(authDetails);
  } catch (e) {
    print(e);
    return;
  }

  final _credentials = CognitoCredentials(_identityPoolId, _userPool);
  await _credentials.getAwsCredentials(_session.getIdToken().getJwtToken());

  final host = 's3.ap-southeast-1.amazonaws.com';
  final region = 'ap-southeast-1';
  final service = 's3';
  final key =
      'my-s3-bucket/ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/square-cinnamon.jpg';
  final payload = SigV4.hashCanonicalRequest('');
  final datetime = SigV4.generateDatetime();
  final canonicalRequest = '''GET
${'/$key'.split('/').map((s) => Uri.encodeComponent(s)).join('/')}

host:$host
x-amz-content-sha256:$payload
x-amz-date:$datetime
x-amz-security-token:${_credentials.sessionToken}

host;x-amz-content-sha256;x-amz-date;x-amz-security-token
$payload''';
  final credentialScope =
      SigV4.buildCredentialScope(datetime, region, service);
  final stringToSign = SigV4.buildStringToSign(datetime, credentialScope,
      SigV4.hashCanonicalRequest(canonicalRequest));
  final signingKey = SigV4.calculateSigningKey(
      _credentials.secretAccessKey, datetime, region, service);
  final signature = SigV4.calculateSignature(signingKey, stringToSign);

  final authorization = [
    'AWS4-HMAC-SHA256 Credential=${_credentials.accessKeyId}/$credentialScope',
    'SignedHeaders=host;x-amz-content-sha256;x-amz-date;x-amz-security-token',
    'Signature=$signature',
  ].join(',');

  final uri = Uri.https(host, key);
  http.Response response;
  try {
    response = await http.get(uri, headers: {
      'Authorization': authorization,
      'x-amz-content-sha256': payload,
      'x-amz-date': datetime,
      'x-amz-security-token': _credentials.sessionToken,
    });
  } catch (e) {
    print(e);
    return;
  }

  final file = File(path.join(
      '/path/to/my/folder',
      'square-cinnamon-downloaded.jpg'));

  try {
    await file.writeAsBytes(response.bodyBytes);
  } catch (e) {
    print(e.toString());
    return;
  }

  print('complete!');
}

For AppSync's GraphQL

Authenticating Amazon Cognito User Pool using JWT Tokens.

import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:amazon_cognito_identity_dart_2/cognito.dart';

void main() async {
  const _awsUserPoolId = 'ap-southeast-1_xxxxxxxxx';
  const _awsClientId = 'xxxxxxxxxxxxxxxxxxxxxxxxxx';

  const _identityPoolId = 'ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx';
  final _userPool = CognitoUserPool(_awsUserPoolId, _awsClientId);

  final _cognitoUser = CognitoUser('+60100000000', _userPool);
  final authDetails =
      AuthenticationDetails(username: '+60100000000', password: 'p@ssW0rd');

  CognitoUserSession _session;
  try {
    _session = await _cognitoUser.authenticateUser(authDetails);
  } catch (e) {
    print(e);
    return;
  }

  final _credentials = CognitoCredentials(_identityPoolId, _userPool);
  await _credentials.getAwsCredentials(_session.getIdToken().getJwtToken());

  final _endpoint =
      'https://xxxxxxxxxxxxxxxxxxxxxxxxxx.appsync-api.ap-southeast-1.amazonaws.com';

  final body = {
    'operationName': 'CreateItem',
    'query': '''mutation CreateItem {
        createItem(name: "Some Name") {
          name
        }
      }''',
  };
  http.Response response;
  try {
    response = await http.post(
      '$_endpoint/graphql',
      headers: {
        'Authorization': _session.getAccessToken().getJwtToken(),
        'Content-Type': 'application/json',
      },
      body: json.encode(body),
    );
  } catch (e) {
    print(e);
  }
  print(response.body);
}

Signing GraphQL requests for authenticated users with IAM Authorization type for access to AppSync data.

import 'package:http/http.dart' as http;
import 'package:amazon_cognito_identity_dart_2/cognito.dart';
import 'package:amazon_cognito_identity_dart_2/sig_v4.dart';

void main() async {
  final credentials = CognitoCredentials(
      'ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', userPool);
  await credentials.getAwsCredentials(session.getIdToken().getJwtToken());

  const endpoint =
      'https://xxxxxxxxxxxxxxxxxxxxxxxxxx.appsync-api.ap-southeast-1.amazonaws.com';

  final awsSigV4Client = AwsSigV4Client(
      credentials.accessKeyId, credentials.secretAccessKey, endpoint,
      serviceName: 'appsync',
      sessionToken: credentials.sessionToken,
      region: 'ap-southeast-1');

  final String query = '''query GetEvent {
    getEvent(id: "3dcd52c3-1fd6-4e4d-8da6-946ef4a0c94d") {
      id
      name
      comments(limit: 10) {
        items {
          content
          createdAt
        }
      }
    }
  }''';

  final signedRequest = SigV4Request(awsSigV4Client,
      method: 'POST', path: '/graphql',
      headers: Map<String, String>.from(
          {'Content-Type': 'application/graphql; charset=utf-8'}),
      body: Map<String, String>.from({
          'operationName': 'GetEvent',
          'query': query}));

  http.Response response;
  try {
    response = await http.post(
        signedRequest.url,
        headers: signedRequest.headers, body: signedRequest.body);
  } catch (e) {
    print(e);
  }
  print(response.body);
}

For API Gateway & Lambda

Signing requests for authenticated users for access to secured routes to API Gateway and Lambda.

import 'package:http/http.dart' as http;
import 'package:amazon_cognito_identity_dart_2/cognito.dart';
import 'package:amazon_cognito_identity_dart_2/sig_v4.dart';

void main() async {
  final credentials = CognitoCredentials(
      'ap-southeast-1:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', userPool);
  await credentials.getAwsCredentials(session.getIdToken().getJwtToken());

  const endpoint =
      'https://xxxx.execute-api.ap-southeast-1.amazonaws.com/dev';
  final awsSigV4Client = AwsSigV4Client(
      credentials.accessKeyId, credentials.secretAccessKey, endpoint,
      sessionToken: credentials.sessionToken,
      region: 'ap-southeast-1');

  final signedRequest = SigV4Request(awsSigV4Client,
      method: 'POST',
      path: '/projects',
      headers: Map<String, String>.from(
          {'header-1': 'one', 'header-2': 'two'}),
      queryParams: Map<String, String>.from({'tracking': 'x123'}),
      body: Map<String, dynamic>.from({'color': 'blue'}));

  http.Response response;
  try {
    response = await http.post(
      signedRequest.url,
      headers: signedRequest.headers,
      body: signedRequest.body,
    );
  } catch (e) {
    print(e);
  }
  print(response.body);
}

Use Custom Storage

Persist user session using custom storage.

Shared Preferences Plugin storage example found here.

import 'dart:convert';
import 'package:amazon_cognito_identity_dart_2/cognito.dart';

Map<String, String> _storage = {};

class CustomStorage extends CognitoStorage {
  String prefix;
  CustomStorage(this.prefix);

  @override
  Future setItem(String key, value) async {
    _storage[prefix+key] = json.encode(value);
    return _storage[prefix+key];
  }

  @override
  Future getItem(String key) async {
    if (_storage[prefix+key] != null) {
      return json.decode(_storage[prefix+key]);
    }
    return null;
  }

  @override
  Future removeItem(String key) async {
    return _storage.remove(prefix+key);
  }

  @override
  Future<void> clear() async {
    _storage = {};
  }
}

final customStore = CustomStorage('custom:');

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
  storage: customStore,
);
final cognitoUser = CognitoUser(
  '[email protected]', userPool, storage: customStore);
final authDetails = AuthenticationDetails(
  username: '[email protected]', password: 'Password001');
await cognitoUser.authenticateUser(authDetails);

// some time later...
final user = await userPool.getCurrentUser();
final session = await user.getSession();
print(session.isValid());

Get AWS credentials with facebook

CognitoCredentials _credential = CognitoCredentials('ap-southeast-1_xxxxxxxxx', userPool);
await _credential.getAwsCredentials(accessToken, 'graph.facebook.com')
print(_credential.sessionToken);

Use client secret

The original amazon-cognito-identity-js which this library is based off, doesn't support client secret. This feature has been added since version 0.1.9, to use it, simply set your client secret when creating CognitoUserPool:

final userPool = CognitoUserPool(
  'ap-southeast-1_xxxxxxxxx',
  'xxxxxxxxxxxxxxxxxxxxxxxxxx',
  clientSecret: 'xxxxxxxxxxxxxxxxxxxxxxx'
);

Flutter web sign-in performance

To improve performance of modPow() used in authenticateUser(), use an external JavaScript call to do the modPow calculation using the native BigInt type.

Include the following JavaScript method in your top level index.html page for your flutter web app.

Also, add package:js as a dependency in your app's pubspec.yaml

js: ^0.6.3

<script>
  function jsBigIntModPow(bStr, eStr, mStr) {
  let b = BigInt(bStr);
  let e = BigInt(eStr);
  let m = BigInt(mStr);
  let bigIntOne = BigInt(1);
  let bigIntZero = BigInt(0);
  if (e < bigIntOne) {
  return bigIntOne;
}
  if (b < bigIntZero || b > m) {
  b = b % m;
}
  var r = bigIntOne;
  while (e > bigIntZero) {
  if ((e & bigIntOne) > bigIntZero) {
  r = (r * b) % m;
}
  e = e >> bigIntOne;
  b = (b * b) % m;
}
  return r;
}
</script>