The AssumeRoleProvider in internal/credproviders constructs it’s STS URI with a hard-coded http://sts.amazqon.com endpoint. This ignores the standard AWS SDK environment variables, so users cannot force the provider to call the regional STS endpoint.

Should we modifying AssumeRoleProvider.RetrieveWithContext so that before formatting stsURI it checks

1. If AWS_STS_REGIONAL_ENDPOIN=regional and
2. If AWS_REGION is set

Then replace the host in the request URL to use the specific region?

It's unlikely other drivers make this check and it adds complexity to our current "bare bones" implementation. However, it's super confusing. This ticket could potentially be closed by GODRIVER-3567 which will offer a pure-AWS SDK solution to this exact problem.