code: func (tc HostCredentialsToken) PrepareRequest(req *http.Request) {
  	if req.Header == nil {
  		req.Header = http.Header{}
  	}
  	req.Header.Set("Authorization", "Bearer "+string(tc))
  }
docs: // PrepareRequest alters the given HTTP request by setting its Authorization
  // header to the string "Bearer " followed by the encapsulated authentication
  // token.