Hello @sakuraime , Happy to help with your questions.
Not sure what speciifc "workspace Post API" you are referencing but here's related API content to get you started. (snipped below)
Check out this content for example on calling log analytics REST API via PowerShell. (snipped below)
Kindly elaborate if there's a speicfic LA API / Operation you wish to invoke and will be happy assist further.
Cheers.
LogAnalytics API Reference Guide (Dev)
LogAnalytics API refrence for PowerShell