I'm working on a website in where some customers have the options to insert UPS Api credentials (key, username and password), and based on those credentials, UPS TimeInTransit and Tracking API are used.
I'm looking for a solution to validate these credentials before storing them for later use.
why do not you make a API request (the smallest one), using the credentials to check the response code. If UPS reply a error, you can also reply the error. If the response it's OK, than store the credentials. Can take a little long, but without that request you will not be able to check the credentials.