verify_async
Description:
public async bool verify_async (Object key, Mechanism mechanism, uint8[] input, uint8[] signature, Cancellable? cancellable) throws Error
  
  Verify data in a mechanism specific manner.
This call returns immediately and completes asynchronously.
Parameters:
| this | 
           The session.  | 
      
| key | 
           The key to verify with.  | 
      
| mechanism | 
           The mechanism type and parameters to use for signing.  | 
      
| input | 
           data to verify  | 
      
| signature | 
           the signature  | 
      
| cancellable | 
           A GCancellable which can be used to cancel the operation.  | 
      
| callback | 
           Called when the operation completes.  | 
      
| n_input | 
           the length of the data to verify  | 
      
| n_signature | 
           the length of the signature  | 
      
| user_data | 
           A pointer to pass to the callback.  |