Added the TokenProvider as a useful tool

tools/react/README.md

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+# TokenProvider
+
+The MERN-template utilizes React's `useContext()` hook to share the auth-server's access token, effectively globally. Here is a quick rundown of how it works.
+
+# Enabling TokenProvider
+
+To enable the TokenProvider component, wrap your App component with it, like so:
+
+```jsx
+import React from 'react';
+import ReactDOM from 'react-dom';
+
+import App from './pages/app';
+import TokenProvider from './pages/utilities/token-provider';
+
+ReactDOM.render(
+	<TokenProvider>
+		<App />
+	</TokenProvider>,
+	document.querySelector('#root')
+);
+```
+
+# Accessing The Access Token
+
+To access the access token from your app, you simply use the `useContext` hook, like so:
+
+```jsx
+import React, { useContext } from 'react';
+import { TokenContext } from '../utilities/token-provider';
+
+const Component = props => {
+	//context
+	const authTokens = useContext(TokenContext);
+
+	//use the access token
+	console.log(authTokens.accessToken);
+
+	return <div />;
+};
+
+export default Component;
+```
+
+# Most Useful Features Provided
+
+The most useful features provided by TokenProvider are:
+
+* `tokenFetch()`, which wraps the `fetch()` API to ensure that your access token is valid
+* `tokenCallback()`, which passes the authTokens as a parameter to any function passed into it
+* `getPayload()`, which returns the payload of the accessToken (including as "email", "username", "admin", and "mod")
+* `accessToken`, this will be falsy if the user is not logged in
+

tools/react/token-provider.jsx

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+import React, { useState, useEffect, createContext } from 'react';
+import decode from 'jwt-decode';
+
+export const TokenContext = createContext();
+
+//DOCS: tokenFetch() and tokenCallback() are actually closures here
+
+const TokenProvider = props => {
+	//state to be used
+	const [accessToken, setAccessToken] = useState('');
+	const [refreshToken, setRefreshToken] = useState('');
+
+	//make the access and refresh tokens persist between reloads
+	useEffect(() => {
+		setAccessToken(localStorage.getItem("accessToken") || '');
+		setRefreshToken(localStorage.getItem("refreshToken") || '');
+	}, []);
+
+	//update the stored copies
+	useEffect(() => {
+		localStorage.setItem("accessToken", accessToken);
+		localStorage.setItem("refreshToken", refreshToken);
+	}, [accessToken, refreshToken]);
+
+	//wrap the default fetch function
+	const tokenFetch = async (url, options) => {
+		//use this?
+		let bearer = accessToken;
+
+		//if expired (10 minutes, normally)
+		const expired = new Date(decode(accessToken).exp * 1000) < Date.now();
+
+		if (expired) {
+			//BUGFIX: if logging out, just skip over the refresh token
+			if (url === `${process.env.AUTH_URI}/auth/logout`) {
+				return fetch(url, {
+					method: 'DELETE',
+					headers: {
+						'Content-Type': 'application/json',
+						'Access-Control-Allow-Origin': '*',
+						'Authorization': `Bearer ${bearer}`
+					},
+					body: JSON.stringify({
+						token: refreshToken
+					})
+				});
+			}
+
+			//ping the auth server for a new token
+			const response = await fetch(`${process.env.AUTH_URI}/auth/token`, {
+				method: 'POST',
+				headers: {
+					'Content-Type': 'application/json',
+					'Access-Control-Allow-Origin': '*'
+				},
+				body: JSON.stringify({
+					token: refreshToken
+				})
+			});
+
+			//any errors, throw them
+			if (!response.ok) {
+				throw `${response.status}: ${await response.text()}`;
+			}
+
+			//save the new auth stuff (setting bearer as well)
+			const newAuth = await response.json();
+
+			setAccessToken(newAuth.accessToken);
+			setRefreshToken(newAuth.refreshToken);
+			bearer = newAuth.accessToken;
+		}
+
+		//finally, delegate to fetch
+		return fetch(url, {
+			...(options || {}),
+			headers: {
+				...(options || { headers: {} }).headers,
+				'Authorization': `Bearer ${bearer}`
+			}
+		});
+	};
+
+	//access the refreshed token via callback
+	const tokenCallback = async (cb) => {
+		//if expired (10 minutes, normally)
+		const expired = new Date(decode(accessToken).exp * 1000) < Date.now();
+
+		if (expired) {
+			//ping the auth server for a new token
+			const response = await fetch(`${process.env.AUTH_URI}/auth/token`, {
+				method: 'POST',
+				headers: {
+					'Content-Type': 'application/json',
+					'Access-Control-Allow-Origin': '*'
+				},
+				body: JSON.stringify({
+					token: refreshToken
+				})
+			});
+
+			//any errors, throw them
+			if (!response.ok) {
+				throw `${response.status}: ${await response.text()}`;
+			}
+
+			//save the new auth stuff (setting bearer as well)
+			const newAuth = await response.json();
+
+			setAccessToken(newAuth.accessToken);
+			setRefreshToken(newAuth.refreshToken);
+
+			//finally
+			return cb(newAuth.accessToken);
+		} else {
+			return cb(accessToken);
+		}
+	};
+
+	return (
+		<TokenContext.Provider value={{ accessToken, refreshToken, setAccessToken, setRefreshToken, tokenFetch, tokenCallback, getPayload: () => decode(accessToken) }}>
+			{props.children}
+		</TokenContext.Provider>
+	)
+};
+
+export default TokenProvider;