OAuth2 PW GRANT

Hi I am trying to use OAuth2 PASSWORD_GRANT in debugging. But can not find any place to add my username and pw. I have tried to put them in the url without success.
I can add client_id and secret in GUI but how do I send user and pw?

https://oauth2.mydomain.com/token?username=My-Debug&password=S3ctret

Any suggestions?

regs
Taisto