code: func (gsa *GServiceAccount) Client(ctxt context.Context, scopes ...string) (*http.Client, error) {
  	b, err := gsa.TokenSource(ctxt, scopes...)
  	if err != nil {
  		return nil, err
  	}
  	return b.Client(), nil
  }
docs: // Client returns a HTTP client using the provided context and scopes for the
  // service account as the underlying transport.
  //
  // When called with the appropriate scopes, the created client can be passed to
  // any Google API for creating a service client:
  //
  // 		import (
  // 			dns "google.golang.org/api/dns/v2beta1"
  //      )
  //      cl, err := gsa.Client(ctxt, dns.CloudPlatformScope, dns.NdevClouddnsReadwriteScope)
  // 		if err != nil { /* ... */ }
  //      dnsService, err := dns.New(cl)
  // 		if err != nil { /* ... */ }
  //
  // Note: this is a convenience func only.