AWS CDK Github OpenID Connect

---

AWS CDK constructs that define:

• Github Actions as OpenID Connect Identity Provider into AWS IAM
• IAM Roles that can be assumed by Github Actions workflows

These constructs allows you to harden your AWS deployment security by removing the need to create long-term access keys for Github Actions and instead use OpenID Connect to Authenticate your Github Action workflow with AWS IAM.

Background information

• GitHub Actions: Secure cloud deployments with OpenID Connect on Github Changelog Blog.
• Security hardening your deployments on Github Docs.
• Assuming a role with aws-actions/configure-aws-credentials.
• Shout-out to Richard H. Boyd for helping me to debug Github OIDC setup with AWS IAM and his Deploying to AWS with Github Actions-talk.
• Shout-out to Aidan W Steele and his blog post AWS federation comes to GitHub Actions for being the original inspiration for this.

Getting started

npm i -D aws-cdk-github-oidc

OpenID Connect Identity Provider trust for AWS IAM

To create a new Github OIDC provider configuration into AWS IAM:

import { GithubActionsIdentityProvider } from "aws-cdk-github-oidc";

const provider = new GithubActionsIdentityProvider(scope, "GithubProvider");

In the background this creates an OIDC provider trust configuration into AWS IAM with an issuer URL of https://token.actions.githubusercontent.com and audiences (client IDs) configured as ['sts.amazonaws.com'] (which matches the aws-actions/configure-aws-credentials implementation).

Retrieving a reference to an existing Github OIDC provider configuration

Remember, there can be only one (Github OIDC provider per AWS Account), so to retrieve a reference to existing Github OIDC provider use fromAccount static method:

import { GithubActionsIdentityProvider } from "aws-cdk-github-oidc";

const provider = GithubActionsIdentityProvider.fromAccount(
  scope,
  "GithubProvider"
);

Defining a role for Github Actions workflow to assume

import { GithubActionsRole } from "aws-cdk-github-oidc";

const uploadRole = new GithubActionsRole(scope, "UploadRole", {
  provider: provider, // reference into the OIDC provider
  owner: "octo-org", // your repository owner (organization or user) name
  repo: "octo-repo", // your repository name (without the owner name)
  filter: "ref:refs/tags/v*", // JWT sub suffix filter, defaults to '*'
});

// use it like any other role, for example grant S3 bucket write access:
myBucket.grantWrite(uploadRole);

You may pass in any iam.RoleProps into the construct's props, except assumedBy which will be defined by this construct (CDK will fail if you do):

const deployRole = new GithubActionsRole(scope, "DeployRole", {
  provider: provider,
  owner: "octo-org",
  repo: "octo-repo",
  roleName: "MyDeployRole",
  description: "This role deploys stuff to AWS",
  maxSessionDuration: cdk.Duration.hours(2),
});

// You may also use various "add*" policy methods!
// "AdministratorAccess" not really a good idea, just for an example here:
deployRole.addManagedPolicy(
  iam.ManagedPolicy.fromAwsManagedPolicyName("AdministratorAccess")
);

Subject Filter

By default the value of filter property will be '*' which means any workflow (from given repository) from any branch, tag, environment or pull request can assume this role. To further stricten the OIDC trust policy on the role, you may adjust the subject filter as seen on the examples in Github Docs; For example:

filter value	Descrition
'ref:refs/tags/v*'	Allow only tags with prefix of v
'ref:refs/heads/demo-branch'	Allow only from branch demo-branch
'pull_request'	Allow only from pull request
'environment:Production'	Allow only from Production environment

Github Actions Workflow

To actually utilize this in your Github Actions workflow, use aws-actions/configure-aws-credentials to assume a role.

At the moment you must use the master version (until AWS releases a new tag):

jobs:
  deploy:
    name: Upload to Amazon S3
    runs-on: ubuntu-latest
    permissions:
      id-token: write # needed to interact with GitHub's OIDC Token endpoint.
      contents: read
    steps:
      - name: Checkout
        uses: actions/checkout@v2

      - name: Configure AWS credentials
        uses: aws-actions/configure-aws-credentials@master
        with:
          role-to-assume: arn:aws:iam::123456789012:role/MyUploadRole
          #role-session-name: MySessionName # Optional
          aws-region: us-east-1

      - name: Sync files to S3
        run: |
          aws s3 sync . s3://my-example-bucket