Greetings of the day!
I can see that you need guidance regarding setting up permission for a user to access Transfer for SFTP.
I would like to mention that you can control a user's access to AWS Transfer Family resources by using an AWS Identity and Access Management (IAM) policy. An IAM policy is a statement, typically in JSON format, that allows a certain level of access to a resource. You use an IAM policy to define what file operations that you want to allow your users to perform and not perform. You can also use an IAM policy to define what Amazon S3 bucket or buckets that you want to give your users access to. To specify these policies for users, you create an IAM role for AWS Transfer Family that has the IAM policy and trust relationship associated with it.
Please refer below documents as they provide detailed information regarding providing access.
[+] Managing access controls - https://docs.aws.amazon.com/transfer/latest/userguide/users-policies.html
[+] Creating a session policy for an Amazon S3 bucket - https://docs.aws.amazon.com/transfer/latest/userguide/users-policies.html#users-policies-session
Further, I request you to open a support case if you need any further assistance.
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