set_pin
Description:
public bool set_pin (uint8[]? old_pin, uint8[]? new_pin, Cancellable? cancellable = null) throws Error
  
  Change the user's pin on this slot that this session is opened on.
This call may block for an indefinite period.
Parameters:
| this | Change the PIN for this session's slot. | 
| old_pin | the user's old PIN, or null for protected authentication path. | 
| new_pin | the user's new PIN, or null for protected authentication path | 
| cancellable | Optional cancellation object, or null. | 
| n_new_pin | The length of the PIN. | 
| n_old_pin | The length of the PIN. | 
Returns:
| Whether successful or not. |