AWS CLI assume role in AWS CodeBuild through ECS credentials

buildspec.yaml

version: '0.2'
phases:
  build:
    commands:
      - |
        cat << EOF > aws_config
        [profile test]
        role_arn = arn:aws:iam::123456789012:role/my-role-to-assume
        role_session_name = IntegrationTest
        credential_source = EcsContainer
        EOF
      - export AWS_CONFIG_FILE=./aws_config
      - aws sts get-caller-identity --profile test # Uses the assumed role