How to automatically populate a customized field of Deal



I have a requirement that we need to populate a unique value for a customized field of deal on creation.
My thought is using webhook, but after some investigation, the webhook is using to integrate some third part software, the point is we don't have such software. So my question is can we build a java project or web service then we use webhook to trigger this project to generate a unique value then call Deal update API back to hubspot .
If we can, how can I add parameter with webhook since we need to send the primary key (deal id) to the project or web service to perform the update.

Much appriciate for your help. Thanks!



@sam You can do this and the primary key(deal id) will be a part of the JSON that is in the body of the webhook request reaching your endpoint/web service. The output will mirror the output from get a deal in our APIs.