How to define OAuth2 ClientCredentials flow with Header parameters and Query parameters

I have an API that is secured by OAuth2 client credentials flow. It takes 3 parameters and returns a token.
1. A subscription key in the header
2. Content type in the header
3. A query in the querystring.

How do I define that in the swagger documentation?

securityDefinitions:
my_auth:
type: "oauth2"
tokenUrl: "https://mytokenURL/graphql"
flow: "application"
scopes:
read:roster: "read your data"

Where do I define that my tokenURL takes 3 parameters (2 in header and 1 in querystring)? Also my tokenURL works with HTTP POST, where can I define that?