what is the token request's query string format

[geminiyellow]

can set Basic Authentication follow this:
https://auth0.com/docs/extensions/custom-social-extensions#optional-set-up-basic-authentication

but what is the custom connections token request's url's query string format? and how to add custom parameter to it?
because authorization server not support including the client credentials in the request-body , i have to set it in the parameter string.