br backup to aliyum OSS not support ak/sk as env

[knull-cn]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. set env AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
2. br full backup --s3.provider "alibaba" --s3.endpoint "xxx" xxxxx

2. What did you expect to see? (Required)

access OSS sucess

3. What did you see instead (Required)

access by RAM first
get AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY by env args was latter by s3 lib

4. What is your TiDB version? (Required)

v7.1.0
(OSS was import in v6.1.0 ,so this bug was in >= v6.1.0)

[knull-cn]

aliyun OSS only use RAM access , but not check env provider first
https://github.com/pingcap/tidb/blob/v6.1.0/br/pkg/storage/s3.go#L266-L273

[3pointer]

Do you mean RAM and AK/SK have different permissions? they are different?
What's the actual error in this scenario?

[BornChanger]

/severity moderate

[BornChanger]

@knull-cn do you mind raising a pr for this issue?

[BornChanger]

/remove-severity major