Support sts_regional_endpoints configuration

[mtibben]

Support the sts_regional_endpoints in the aws config file or via the AWS_STS_REGIONAL_ENDPOINTS env var.

Reference: https://docs.aws.amazon.com/cli/latest/topic/config-vars.html#aws-sts

This may help with #543

[ronkorving]

@mtibben How do I enable this as a user from my config file? This should make AWS Vault run a bit faster for us on the other side of the planet (of us-east-1) I guess. But it's not entirely clear for me from the doc update in this PR on how to do this in my config file.

I've tried

sts_regional_endpoints = regional

But when I execute aws vault exec myprofile -- env |grep AWS I do not see AWS_STS_REGIONAL_ENDPOINTS getting set. Does it only apply to the inner workings of AWS Vault and not set an env var for whatever I end up executing next? If it only applies to internals, is there a way for me to confirm I've configured it right?

[mtibben]

Yep try with --debug

[ronkorving]

Works! Awesome! Thank you :)