automating OAuth2 token retrieval

I read through all the documentation for OAuth2, here.

My case uses the "Client Credentials Grant" method. Doing things manually - clicking the Get Access Token button - everything works fine.

In order to automate this, how do I "click" the Get Access Token button? I read through the documentation, but I do not have any "pages" to deal with. I just click the Get Access Token button and that is it.