From upstream tracker:

When having obtained temporary credentials using STS (AssumeRole), I can use these temp credentials to copy files from local machine to ceph and vice versa, but I cannot copy files within a bucket (server-side copy). When attempting the same server-side copy operation using the permanent credentials which were used in calling the AssumeRole command, it succeeds.

The AssumeRolePolicy document of the role is:

{\"Version\":\"2012-10-17\",\"Statement\":[{\"Effect\":\"Allow\",\"Principal\":{\"AWS\":\"arn:aws:iam:::user/129-9bef358e31a44f85b8a84880c459def9\"},\"Action\":\"sts:AssumeRole\"}]}
The permission policy attached to the role is (I've made this as permissive as possible to try to fix the problem without success):

{\"Version\":\"2012-10-17\",\"Statement\":{\"Effect\":\"Allow\",\"Action\":[\"s3:*\"],\"Resource\":\"arn:aws:s3:::*\"}}
The request and response when attempting the server-side copy are shown here:

2020/09/23 16:26:49 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2020/09/23 16:26:49 DEBUG : HTTP REQUEST (req 0xc0006e8200)
2020/09/23 16:26:49 DEBUG : PUT /129-73b1a5466f424d33b39d5b616fb39166/134/18/68copy/home/test/Documents/Testing/rsyncTestingB/test1/loadings/test1.txt HTTP/1.1
Host: redacted
User-Agent: rclone/v1.52.2-232-gff843516-beta
Content-Length: 0
Authorization: XXXX
X-Amz-Acl: private
X-Amz-Content-Sha256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
X-Amz-Copy-Source: 129-73b1a5466f424d33b39d5b616fb39166/134/18/68/home/test/Documents/Testing/rsyncTestingB/test1/loadings/test1.txt
X-Amz-Date: 20200923T142649Z
X-Amz-Metadata-Directive: COPY
X-Amz-Security-Token: redacted=
Accept-Encoding: gzip
2020/09/23 16:26:49 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

2020/09/23 16:26:49 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2020/09/23 16:26:49 DEBUG : HTTP RESPONSE (req 0xc0006e8200)
2020/09/23 16:26:49 DEBUG : HTTP/2.0 403 Forbidden
Content-Length: 250
Accept-Ranges: bytes
Content-Type: application/xml
Date: Wed, 23 Sep 2020 14:26:49 GMT
X-Amz-Request-Id: tx0000000000000000001de-005f6b5b29-442aa9-default

<Error><Code>AccessDenied</Code><BucketName>129-73b1a5466f424d33b39d5b616fb39166</BucketName><RequestId>tx0000000000000000001de-005f6b5b29-442aa9-default</RequestId><HostId>442aa9-default-default</HostId></Error>
2020/09/23 16:26:49 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

In case it helps, as can be seen in the request, I am using rclone for doing the actual transfer.