Change grant_type password to client_credentials, add scope and client_secret

[Fosten]

• Password grant is no longer supported. Adds client_credentials.
• Adds option for scope
• Adds option for client_secret

[braughtg]

Awesome @Fosten :-) but... you can enable that contrib module to get password credentials as an option.

It would be great to have both. I use the password credentials quite a bit in my test suite and it would be nice not to have to rebuild all of that.