/**
 * Reject a region that is not a single hostname label. The region is
 * interpolated into the host (`<service>.<region>.amazonaws.com`) that the
 * SigV4 signature and any session token are sent to, so a value such as
 * `x.evil.example/` would redirect the credentials. Checked the way botocore
 * checks it, before any request is signed.
 */
export declare function assertAwsRegion(region: unknown, service: string): void;