How to use Redux to refresh JWT token?

I found a way to solve this. I am not sure if this is best practice approach and there are probably some improvements that could be made to it.

My original idea stays: JWT refresh is in the middleware. That middleware has to come before thunk if thunk is used.

...
const createStoreWithMiddleware = applyMiddleware(jwt, thunk)(createStore);

Then in the middleware code we check to see if token is expired before any async action. If it is expired we also check if we are already are refreshing the token -- to be able to have such check we add promise for fresh token to the state.

import { refreshToken } from '../actions/auth';

export function jwt({ dispatch, getState }) {

    return (next) => (action) => {

        // only worry about expiring token for async actions
        if (typeof action === 'function') {

            if (getState().auth && getState().auth.token) {

                // decode jwt so that we know if and when it expires
                var tokenExpiration = jwtDecode(getState().auth.token).<your field for expiration>;

                if (tokenExpiration && (moment(tokenExpiration) - moment(Date.now()) < 5000)) {

                    // make sure we are not already refreshing the token
                    if (!getState().auth.freshTokenPromise) {
                        return refreshToken(dispatch).then(() => next(action));
                    } else {
                        return getState().auth.freshTokenPromise.then(() => next(action));
                    }
                }
            }
        }
        return next(action);
    };
}

The most important part is refreshToken function. That function needs to dispatch action when token is being refreshed so that the state will contain the promise for the fresh token. That way if we dispatch multiple async actions that use token auth simultaneously the token gets refreshed only once.

export function refreshToken(dispatch) {

    var freshTokenPromise = fetchJWTToken()
        .then(t => {
            dispatch({
                type: DONE_REFRESHING_TOKEN
            });

            dispatch(saveAppToken(t.token));

            return t.token ? Promise.resolve(t.token) : Promise.reject({
                message: 'could not refresh token'
            });
        })
        .catch(e => {

            console.log('error refreshing token', e);

            dispatch({
                type: DONE_REFRESHING_TOKEN
            });
            return Promise.reject(e);
        });



    dispatch({
        type: REFRESHING_TOKEN,

        // we want to keep track of token promise in the state so that we don't try to refresh
        // the token again while refreshing is in process
        freshTokenPromise
    });

    return freshTokenPromise;
}

I realize that this is pretty complicated. I am also a bit worried about dispatching actions in refreshToken which is not an action itself. Please let me know of any other approach you know that handles expiring JWT token with redux.

Instead of "waiting" for an action to finish, you could instead keep a store variable to know if you're still fetching tokens:

Sample reducer

const initialState = {
    fetching: false,
};
export function reducer(state = initialState, action) {
    switch(action.type) {
        case 'LOAD_FETCHING':
            return {
                ...state,
                fetching: action.fetching,
            }
    }
}

Now the action creator:

export function loadThings() {
    return (dispatch, getState) => {
        const { auth, isLoading } = getState();

        if (!isExpired(auth.token)) {
            dispatch({ type: 'LOAD_FETCHING', fetching: false })
            dispatch(loadProfile());
            dispatch(loadAssets());
       } else {
            dispatch({ type: 'LOAD_FETCHING', fetching: true })
            dispatch(refreshToken());
       }
    };
}

This gets called when the component mounted. If the auth key is stale, it will dispatch an action to set fetching to true and also refresh the token. Notice that we aren't going to load the profile or assets yet.

New component:

componentDidMount() {
    dispath(loadThings());
    // ...
}

componentWillReceiveProps(newProps) {
    const { fetching, token } = newProps; // bound from store

    // assuming you have the current token stored somewhere
    if (token === storedToken) {
        return; // exit early
    }

    if (!fetching) {
        loadThings()
    } 
}

Notice that now you attempt to load your things on mount but also under certain conditions when receiving props (this will get called when the store changes so we can keep fetching there) When the initial fetch fails, it will trigger the refreshToken. When that is done, it'll set the new token in the store, updating the component and hence calling componentWillReceiveProps. If it's not still fetching (not sure this check is necessary), it will load things.