How to Secure JWT in a Single-Page Application

Securely make JWT based authentication in React Application.

In this article, we will see how to securely store the JWT token in a single page app for authentication.

What are all the options we have to store the token in the browser?

1. Local storage
2. Memory
3. Cookie

JWT in Local Storage

Is local storage is secure to store a token? Let see now, Local storage is accessible from client-side only, so your API provider will set the JWT in the API response Authorization header as a bearer token in login or Register API if the status success. In React, we will get the JWT and store it in the local storage as below

And for the subsequent request made from the react app, the JWT is taken from local storage and set in the API request Authorization header to maintain the user session

Values in local storage are accessible by javascript, so any cross-site script can get the JWT from local storage and gain your account access.

So we should not use local storage for storing JWT if you are using, Please update your authentication architecture as local storage is not secure to store a token. Next, let's move to memory

JWT in Memory (React State)

React state variables will be assigned to default values when the app is refreshed or opened in a new tab, so if the default values are null, when the app is refreshed or opened in a new tab it will be set to null, so when we set the JWT in state variable it will disappear, so the user need to log in each time the app is refreshed or opened in a new tab or the app is closed, it will be poor User Experience. So we cannot store the JWT in the state variable.

Before moving to JWT in cookie, Let’s see about what is a cookie and its major attributes

Cookie

A cookie is another storage option available in a browser which has a expire time also, cookie also have some useful attributes to secure it from cross-site scripting (XSS) attacks. Let see what are they in detail

HttpOnly

A cookie with HttpOnly attribute is not accessible by Javascript, so we cannot get the cookie as below

let cookie= document.cookie; 

HttpOnly cookie can be set and accessed only by the server-side script. This attribute helps to prevent cross-site scripting(XSS) attacks if it’s set with SameSite=strict.

Secure

A cookie with Secure attribute will be sent to the server only over the HTTPS request, not in an HTTP request. The Secure cookie is encrypted in request and response, so Man-in-the-middle attack is prevented by using Secure attribute with HttpOnly and SameSite=strict.

SameSite

A cookie with SameSite=strict mentions that the cookie is available only for same site origin request not for cross-site request. Now let see how to use the cookie to store JWT.

JWT in Cookie

A cookie can be set from the server-side and also in client-side, First we can see how to set and get the JWT from the cookie in the React and using the browser console.

The server set the JWT as a Bearer token in the Authorization response header, In client-side, the script has access to the token present in the header, we get the token from response header and set in the cookie as below

The cookie is set to the current domain by default and expiry date is set to 1st Jan 2021. The expiry date is based on the token validity so the token will be removed from browser cookie once the expiry date reaches.

The cookie needs to send as a bearer token in API request header on every request made from the client. So, for that, we can get it from the cookie using document.cookie property as below

document.cookie will return all cookies present against the domain, so we can use react-cookie package to get a specific cookie as below

As we can see that the token is set and get using the script, so we could conclude that handling JWT in the react will lead to XSS (Cross-Site Scripting) attacks same as we saw before while using local storage, but we saw two attributes earlier HttpOnly and Secure, by setting these attributes will avoid these attacks. But javascript has no access to HttpOnly attribute, Only server-side script can access HttpOnly attributes. Let see how we can set the JWT from Server Side.

As previous examples, we saw that JWT is set as Bearer token in authorization header, But handling cookie in server-side we need set the cookie in Set-Cookie header and not required to mention the token type as Bearer, we can set the JWT directly in Set-Cookie.

Here I am using Express.js to set JWT in the cookie from the server and we have set secure and HttpOnly as true to restrict the javascript access of JWT in the cookie as below

The token in API response Set-Cookie header will be saved to browser cookies like in below image

JWT stored in the cookie will be appended in every API request headers automatically as below images

But remember that this approach only works if the React app and the BackEnd server hosted in same domain.

Now your app is secured from Cross-Site Scripting (XSS) attacks.

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