AWS Signature Version 4 #

An HTTP request signer for AWS Signature Version 4, which can be used to communicate with AWS services. Works in Web, VM, and Flutter projects.

Using the Signer #

To get started using the signer, add it as a dependency in your pubspec.yaml and create an instance in your project.

dependencies:
  aws_common: ^0.3.0
  aws_signature_v4: ^0.3.0

import 'package:aws_signature_v4/aws_signature_v4.dart';

const signer = AWSSigV4Signer();

AWS credentials are configured in the signer by overriding the credentialsProvider parameter of the constructor. By default, the signer pulls credentials from your environment via the AWSCredentialsProvider.environment() provider. On mobile and web, this means using the Dart environment which is configured by passing the --dart-define flag to your flutter commands, e.g.

$ flutter run --dart-define=AWS_ACCESS_KEY_ID=... --dart-define=AWS_SECRET_ACCESS_KEY=...

On Desktop, credentials are retrieved from the system's environment using Platform.environment.

The signer works by transforming HTTP requests using your credentials to create signed HTTP requests which can be sent off in the same way as normal HTTP requests.

Example #

As an example, here's how you would sign a request to Cognito to gather information about a User Pool.

import 'dart:convert';

import 'package:aws_common/aws_common.dart';
import 'package:aws_signature_v4/aws_signature_v4.dart';

// Create the signer instance with credentials from the environment.
const signer = AWSSigV4Signer(
  credentialsProvider: AWSCredentialsProvider.environment(),
);

// Create the signing scope and HTTP request
const region = '<YOUR-REGION>';
final scope = AWSCredentialScope(
  region: region,
  service: AWSService.cognitoIdentityProvider,
);
final request = AWSHttpRequest(
  method: AWSHttpMethod.post,
  uri: Uri.https('cognito-idp.$region.amazonaws.com', '/'),
  headers: const {
    AWSHeaders.target: 'AWSCognitoIdentityProviderService.DescribeUserPool',
    AWSHeaders.contentType: 'application/x-amz-json-1.1',
  },
  body: json.encode({
    'UserPoolId': '<YOUR-USER-POOL-ID>',
  }).codeUnits,
);

// Sign and send the HTTP request
final signedRequest = await signer.sign(
  request,
  credentialScope: scope,
);
final resp = await signedRequest.send();
final respBody = await resp.decodeBody();
safePrint(respBody);

For a full example, check out the example project in the GitHub repo. And for specifics on the different AWS operations you can perform, check out the AWS API Reference docs for the service. For example, here are the docs for the DescribeUserPool API used above.

Testing #

1. Make sure you have pulled down this repository's submodules

git submodule update --init

2. Run dart test