Expression Language support in AmazonS3

[Venkateswara Rachapudi]

Hello,
I saw that  Access Key and Secret key does not support expression language
https://stackoverflow.com/questions/43646105/how-to-configure-nifi-puts3object-processor-to-use-flow-attributes-for-s3-creden

My question is why AmazonS3 Processor doesn’t support expression language 
where as I have configured the Access key and Secret Key using Expression 
Language for Azure Blob in NIFI.