As seen on figure, the request parameters first sent to Service B, after successful authorization, request parameters are sent to Service A (the target service).
The output is verified with one of the request parameters. Authorication succeed if the output is same as the value of the specified parameter.
'Not Equals' Verification
The output of the executable service is checked if it is not equals a predefined text value.
If the executable prints "NOK" for incorrect parameters and print a generated ID for correct parameters (unpredictable value), you can use "NOK" with 'Not Equals' verification.
Numeric Expression Verification