Support ECS ram role authentication

[jerrychenhf]

The code in core.py showed that the current implementation doesn't support ECS ram role authentication.
The capability is provided by oss2 with the combination of ProviderAuth and EcsRamRoleCredentialsProvider.
This is a very important authentication scenario and we hope this ossfs can prioritize the support.

[karajan1001]

Hi, @jerrychenhf.
Sorry for late, a lot of things happened to me in the past two months. I want to make sure #83 meets your feature request.

[jerrychenhf]

@karajan1001 Thank you for taking time to address the feature request.
#82 will work by passing an auth object. While considering using ECS role authentication is a very common use case, one approach is passing a role name (empty role name for auto retrieve from meta server) as a parameter similar to secrets or token, and handling wrapper the EcsRamRoleCredentialsProvider code within the fs object. This will make the user code simpler. More important, some libraries wrappers fsspec such as PetaStorm for AI training cases and string value options is preferred to passing auth object because the options may be pickled or unpickled for remote execution.

[karajan1001]

@jerrychenhf
Hello, jerrychen, I'm sorry I didn't find any info in the official docs about this EcsRamRoleCredentialsProvider. The test case in #82 I provided is copied from the python-sdk test example in https://github.com/aliyun/aliyun-oss-python-sdk/blob/fadfabbbdddd2b40c9da714a045ea59acd7bcab8/tests/test_credentials_provider.py#L22.
I had some confusion here:
If I want to use a security token to log in, then of cause I don't need an arn name for it. And, it is also enough only to use a signed_url to log in. I'm not sure what is your typical use case here, could you please provide some examples for me? Thank you