How to add S3 BucketPolicy with AWS CDK

Question

I wanna translate this CloudFormation piece into CDK:

Type: AWS::S3::BucketPolicy
Properties:
  Bucket:
    Ref: S3BucketImageUploadBuffer
  PolicyDocument:
    Version: "2012-10-17"
    Statement:
      Action:
        - s3:PutObject
        - s3:PutObjectAcl
      Effect: Allow
      Resource:
        - ...

Looking at the documentation here, I don't see a way to provide the policy document itself.