I have a function that allows the end user to execute a Workflow
(containing many APIs) or schedule it to run as a background job.
Example: User1
You have two options.
1- You can make those Application Services anonymously accessible. And if you want it to be secure, send an encrypted security token.
2- You didn't mention if your project is MVC or Angular. I assume you have Angular version. You need a bearer token to make authenticated requests. First you have to authenticate user and get a token. Then add this bearer token to every request.
You have to research for using bearer tokens in asp.net core...