CloudFront distribution can't access S3 bucket for website static assets

The problem

I'm trying to deploy an S3 bucket hosting my static website asset and a cloudfront distribution to access it, but the distribution still return a bare xml file for an 'access denied' error:

<Error>
  <Code>AccessDenied</Code>
  <Message>Access Denied</Message>
  <RequestId>5N0Z412GZ0VGV79E</RequestId>
  <HostId>GkpQbOpKeDiaCdFJM7kDq6ouWL/dvdijNu7NseC7KeIIogNabowVrDcfjPZ0xajKpDTx3SmgoEI=</HostId>
</Error>

As this docs page states in the blue Notice alert, I've not made the bucket a website endpoint, this way I can use an OAC to restrict access to its content.

A strange thing is that checking the distribution origin from the web console I see this blue alert, but the copyable policy is the same I found in the bucket permission at the given link.

I have no error during deploy, so it must be a silly configuration error, but it keeps giving me headaches since a week now and I can't figure out what is wrong.

Bucket and object owners corresponds

Since mi website assets are uploaded to the bucket from a different project/pipeline i followed this guide to check if the bucket and the object owners were different but actually corresponds:

> aws s3api list-buckets --query Owner.ID
"3fdbd1e5cad4dd2bbf4c66a3dbaded6b888fdb67ff6aa6e66203a4107fe17b72"

> aws s3api list-objects --bucket my-test-bucket --prefix index.html
{
    "Contents": [
        {
            "Key": "index.html",
            "LastModified": "2023-01-20T11:05:38+00:00",
            "ETag": "\"52f2df5ddf8c35391f3f15a7614def58\"",
            "Size": 325,
            "StorageClass": "STANDARD",
            "Owner": {
                "ID": "3fdbd1e5cad4dd2bbf4c66a3dbaded6b888fdb67ff6aa6e66203a4107fe17b72"
            }
        }
    ]
}

CloudFormation template

Resources:

  BucketPolicy:
    Type: 'AWS::S3::BucketPolicy'
    DependsOn:
      - AppBucket
      - CloudFrontDistribution
    Properties:
      Bucket: !Ref AppBucket
      PolicyDocument:
        Id: MyPolicy
        Version: '2012-10-17'
        Statement:
          Sid: PolicyForCloudFrontPrivateContent
          Action: s3:GetObject
          Effect: Allow
          Principal:
            Service: cloudfront.amazonaws.com
          Condition:
            StringEquals:
              AWS:SourceArn: !Sub arn:aws:cloudfront::${AWS::AccountId}:distribution/${CloudFrontDistribution}
          Resource: !Sub arn:aws:s3:::${AppBucket}/*

  CloudFrontDistribution:
    Type: AWS::CloudFront::Distribution
    DependsOn:
      - AppBucket
      - DefaultCachePolicy
      - DistributionOAC
    Properties:
      DistributionConfig:
        Enabled: true
        Origins:
          - Id: AppBucket
            DomainName: !GetAtt AppBucket.DomainName
            OriginPath: /*
            S3OriginConfig: {}
            OriginAccessControlId: !Ref DistributionOAC
        DefaultRootObject: index.html
        DefaultCacheBehavior:
          ViewerProtocolPolicy: redirect-to-https
          TargetOriginId: AppBucket
          CachePolicyId: !Ref DefaultCachePolicy

  DistributionOAC:
    Type: AWS::CloudFront::OriginAccessControl
    Properties: 
      OriginAccessControlConfig: 
          Name: ExampleOAC
          OriginAccessControlOriginType: s3
          SigningBehavior: always
          SigningProtocol: sigv4

  AppBucket:
    Type: 'AWS::S3::Bucket'
    Properties:
      BucketName: 'test-spa-stack-bucket-app'
      PublicAccessBlockConfiguration:
        BlockPublicAcls : false
        BlockPublicPolicy : false
        IgnorePublicAcls : false
        RestrictPublicBuckets : false
              
  DefaultCachePolicy:
    Type: AWS::CloudFront::CachePolicy
    Properties: 
      CachePolicyConfig: 
        Name: test-cache-policy
        DefaultTTL: 10
        MaxTTL: 10
        MinTTL: 1
        ParametersInCacheKeyAndForwardedToOrigin: 
            CookiesConfig: 
              CookieBehavior: none
            EnableAcceptEncodingBrotli: true
            EnableAcceptEncodingGzip: true
            HeadersConfig: 
              HeaderBehavior: none
            QueryStringsConfig: 
              QueryStringBehavior: none

I had the same error. In my case I had set the default root object on the Distribution (General > Settings) to /index.html and I also set the origin path (Origins > my s3 origin) to /index.html. I only needed to set the object as index.html on the Distribution for it to start responding as expected.

This helped me discover the problem.