How to pass a custom body on token refresh request

Hello!

I have a question about usage this module.
My authentication API is using OAuth 2.0 protocol and to refresh a token I need pass some key/value params on the body.

Example:

```
{
"client_id": CLIENT_ID,
"client_secret": CLIENT_SECRET,
"grant_type": "refresh_token",
"refresh_token": "A_VERY_BIG_STRING"
}
```

Code example:

```
export const attemptTokenRefresh = () => {
return async (dispatch, getState) => {
const state = getState();
dispatch({
[CALL_API]: {
endpoint: '/auth/oauth2_token',
method: 'POST',
body: {
client_id: CLIENT_ID,
client_secret: CLIENT_SECRET,
grant_type: 'refresh_token',
refresh_token: state.auth.refresh_token
},
types: [
ActionTypes.TOKEN_REFRESH_REQUEST,
ActionTypes.TOKEN_REFRESH_SUCCESS,
ActionTypes.TOKEN_REFRESH_FAILURE
]
}
});
};
};
```

I'm passing this parameters at the *attemptTokenRefresh* action, but I don't know if it's the best way to do that. What you think?

The entry point named is the attemptTokenRefresh action, which dispatches CALL_API with a POST body. First determine from the module’s middleware/API contract whether caller-supplied refresh parameters are supported; done means the supported usage is clear and verified for the OAuth 2.0 example.

Written by the indexing model from the issue text.