Must be "refresh_token" to emphasize that you are trying to exchange a refresh token.
client_id
The client id given during the client registration. Alternatively this can be supplied using the Basic HTTP header with the client_id as username and client_secret as password.
client_secret
The client secret given during the client registration. Alternatively this can be supplied using the Basic HTTP header with the client_id as username and client_secret as password.
refresh_token
The refresh token from the access token to refresh.
