How to Test SalesForce Key Product and Consumer Secret

Question

We have a system in which we want to withdraw records (for example, Contact, Account, Opportunity) from our system in SalesForce.

For this, we used ForceToolKit for .Net . We successfully promote contacts from our system in Salesforce.

The first customer must provide the consumer key and private key, and after providing this information, the user will be redirected to the Salesforce for OAuth login page. We save the RefreshToken and it will be used during the push of Data.

Here, if the user provides the wrong consumer key, he is redirected to the Salesforce login page and displays the message below:

error = invalid_client_id & error_description = client% 20identifier% 20invalid

Now we need to check the consumer’s key and secret code before redirecting it to the Salesforce URL and checking whether it is valid or not.

Can someone help me on how to achieve this?