Login & Auth Workflows
WebApp Native Login To Backend With JWTs And Refresh Tokens
By Brian Pontarelli
This workflow is used by web applications using a native login form inside a webapp. This login form POST
s the user’s credentials (email and password) to the backend of the application. The application backend in turn calls to FusionAuth. Below is a diagram that describes the primary components of this workflow and how they interact. Keep in mind that not every interaction is covered here, just the primary login interactions. At the bottom of the diagram is a discussion of the key steps.
For all of our examples, we use a store and a forum for the same company. The store requires a user to log in to view their shopping cart and the forum requires the user to log in to view forum posts. We also provide a couple of example attack vectors that hackers could use if portions of the system are compromised. These cases might be theoretical or based on known exploits such as XSS (cross-site scripting).
Diagram
Legend
() --> request/response bodies
{} --> request parameters
[] --> cookies
Explanation
- The browser requests the shopping cart webapp's homepage from the application backend
- The application backend responds with the HTML, CSS & JavaScript of the homepage
- The user clicks the login link and the browser requests the login page from the application backend
- The application backend responds with the HTML, CSS & JavaScript of the login page (including the form)
- The user inputs their credentials and clicks the submit button. The browser
POST
s the form data to the application backend - The application backend calls the Login API in FusionAuth by passing in the credentials it received
- FusionAuth returns a 200 status code stating that the credentials were okay. It also returns the User object, a JWT and a refresh token in JSON
- The application backend receives the 200 from FusionAuth. It returns a redirect to the browser instructing it to navigate to the user's shopping cart. The JWT and refresh token from FusionAuth are written back to the browser in HTTP cookies. These cookies are HttpOnly, which prevents JavaScript from accessing them, making them less vulnerable to theft. Additionally, all requests from the browser to the application backend will include these cookies so that the backend can use them
- The browser requests the user's shopping cart from the application backend and includes the JWT and refresh token cookies
- The application backend verifies the JWT and then uses the JWT to identify the user. Once the user is identified, the backend looks up the user's shopping cart from the database (or similar location). Finally, the application backend returns the user's shopping cart as HTML, CSS & JavaScript that the browser renders
- A while later, the user's JWT expires and the user clicks on their shopping cart again. The browser requests the shopping cart from the application backend and sends the JWT and refresh token to the application backend
- The application backend verifies the JWT and realizes it is expired. Since the browser also sent across the refresh token, the application backend calls the JWT refresh API in FusionAuth with the refresh token.
- FusionAuth looks up the refresh token and returns a new JWT
- The application backend responds with the user's shopping cart HTML, CSS & JavaScript that the browser renders. It also includes the new JWT as a cookie that replaces the old JWT in the browser
- A while later, the user's refresh token expires and the user clicks on their shopping cart again. The browser requests the shopping cart from the application backend and sends the JWT and refresh token to the application backend
- The application backend verifies the JWT and realizes it is expired. Since the browser also sent across the refresh token, the application backend calls the JWT refresh API in FusionAuth with the refresh token
- Since the refresh token has expired, FusionAuth returns a 404 status code
- Since FusionAuth returned a 404 status code, the application backend returns a redirect to the browser that sends the user to the login page
- The user can log in the same way they did above
- The browser requests the forum webapp's homepage from the application backend. This is a standard SSO login, but because of the way this workflow manages cookies and identities, FusionAuth does not provide SSO capabilities automatically
- The application backend responds with the HTML, CSS & JavaScript of the homepage
- The user clicks the login link and the browser requests the login page from the application backend
- The application backend responds with the HTML, CSS & JavaScript of the login page (including the form)
- The user inputs their credentials and clicks the submit button. The browser
POST
s the form data to the application backend - The application backend calls the Login API in FusionAuth by passing in the credentials it received
- FusionAuth returns a 200 status code stating that the credentials were okay. It also returns the User object, a JWT and a refresh token in JSON
- The application backend receives the 200 from FusionAuth. It returns a redirect to the browser instructing it to navigate to the user's forum posts. The JWT and refresh token from FusionAuth are written back to the browser in HTTP cookies. These cookies are HttpOnly, which prevents JavaScript from accessing them, making them less vulnerable to theft. Additionally, all requests from the browser to the application backend will include these cookies so that the backend can use them
- The browser requests the user's forum posts from the application backend and includes the JWT and refresh token cookies
- The application backend verifies the JWT and then uses the JWT to identify the user. Once the user is identified, the backend looks up the user's forum posts from the database (or similar location). Finally, the application backend returns the user's forum posts as HTML, CSS & JavaScript that the browser renders
- This is an attack vector where the attacker has stolen the user's refresh token. Here, the attacker requests the user's shopping cart with the stolen refresh token and an invalid JWT
- The application backend verifies the JWT and realizes it is invalid. Since the browser also sent across the refresh token, the application backend calls the JWT refresh API in FusionAuth with the refresh token
- FusionAuth looks up the refresh token and returns a new JWT
- The application backend uses the JWT to look up the user's shopping cart. It responds to the attacker with the user's shopping cart HTML, CSS & JavaScript. It also includes the new JWT as a cookie that attacker can now use
- This is an attack vector where the attacker has stolen the user's JWT. Here, the attack requests the user's shopping cart with the stolen JWT
- The application backend verifies the JWT and then uses the JWT to identify the user. Once the user is identified, the backend looks up the user's shopping cart from the database (or similar location). Finally, the application backend returns the user's shopping cart as HTML, CSS & JavaScript to the attacker
Security considerations
This workflow is one of the more secure methods of authenticating users. One downside is that the application backend receives passwords from the browser. While this isn’t an issue if TLS is used and the passwords are not stored by the application backend, developers that do not want to be part of the password chain of responsibility should consider other workflows.
APIs used
Here are the FusionAuth APIs used in this example: