code: func (rs *RSASigner) Verify(buf, sig []byte) ([]byte, error) {
  	var err error
  
  	// decode
  	dec, err := b64.DecodeString(string(sig))
  	if err != nil {
  		return nil, err
  	}
  
  	// verify
  	err = rs.VerifyBytes(buf, dec)
  	if err != nil {
  		return nil, err
  	}
  
  	return dec, nil
  }
docs: // Verify creates a signature for buf, comparing it against the URL-safe base64
  // encoded sig and returning the decoded signature. If the sig is invalid, then
  // ErrInvalidSignature will be returned.