Add a mechanism to read AWS S3 access credentials from environment variables

[DeflateAwning]

Is your feature request related to a problem? Please describe.

In a deployment on AWS, I'd like to manage the S3 bucket access controls through IAM via policy, which generates the access credentials as environment variables.

Describe the solution you'd like

I'd like to be able to type something like [ENV_VAR:AWS_ACCESS_KEY] in the text fields to setup an S3 virtual folder, and have SFTPGo read the environment variable for those fields as such.

Describe alternatives you've considered

Currently you have to generate an insecure IAM user (against all the AWS warnings as you go through the process), and then paste in the secret values. These values aren't automatically rotated though, and have to enter the clipboard of developers.

If this already exists, I couldn't find it in the docs.

What are you using SFTPGo for?

Medium business

Additional context