Starting today, AWS Security Token Service is announcing support for AWS PrivateLink in Asia Pacific (Hong Kong), Asia Pacific (Mumbai), Asia Pacific (Osaka), Asia Pacific (Seoul), Asia Pacific (Singapore), Asia Pacific (Sydney), Canada (Central), EU (Frankfurt), EU (London), EU (Paris), EU (Stockholm), South America (Sao Paolo), and US West (N. California) regions, enabling you to route data between your Amazon Virtual Private Cloud (VPC) and Security Token Service entirely within the AWS network. 

from Recent Announcements: https://aws.amazon.com/about-aws/whats-new/2019/12/aws-security-token-service-now-supports-aws-privatelink-in-13-new-regions/