Login & Auth Workflows
WebApp OAuth Login Using Resource Owner Password Credentials Grant With Sessions And Refresh Tokens
By Brian Pontarelli
This workflow is used by web applications using the FusionAuth OAuth login interface. The web application navigates over to FusionAuth and then FusionAuth redirects back to the web application at the end of the OAuth workflow. 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 login to view their shopping cart and the forum requires the user to login 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 OAuth token endpoint in FusionAuth by passing in the credentials it received plus a
grant_type
ofpassword
, which indicates it is using the resource owner password credentials grant in FusionAuth's OAuth 2 backend - FusionAuth returns a 200 status code stating that the credentials were okay. It also returns a JWT and a refresh token in JSON
- The application backend receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
- The application backend returns a redirect to the browser instructing it to navigate to the user's shopping cart. The id for the server-side session is written back to the browser in an HTTP cookie. The refresh token from FusionAuth is also written back to the browser in an HTTP cookie. 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 retrieve the User object from the server-side session and refresh their session if it expires
- The browser requests the user's shopping cart from the application backend and includes the session and refresh token cookies
- The application backend looks up the server-side session associated with the session cookie and extends the expiration date
- The application backend loads the User object (or JWT) from the server-side session. The backend then 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 session expires and the user clicks on their shopping cart again. The browser requests the shopping cart from the application backend and sends the session id and refresh token cookies to the application backend
- The application backend attempts to load the server-side session associated with session cookie 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 receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
- The application backend responds with the user's shopping cart HTML, CSS & JavaScript that the browser renders. It also includes the new session id as a cookie that replaces the old session id in the browser
- A while later, the user's server-side session and refresh token both expire and the user clicks on their shopping cart again. The browser requests the shopping cart from the application backend and sends the session and refresh token cookies to the application backend
- The application backend attempts to load the server-side session associated with session cookie 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 OAuth token endpoint in FusionAuth by passing in the credentials it received plus a
grant_type
ofpassword
, which indicates it is using the resource owner password credentials grant in FusionAuth's OAuth 2 backend - FusionAuth returns a 200 status code stating that the credentials were okay. It also returns a JWT and a refresh token in JSON
- The application backend receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
- The application backend returns a redirect to the browser instructing it to navigate to the user's forum posts. The id for the server-side session is written back to the browser in an HTTP cookie. The refresh token from FusionAuth is also written back to the browser in an HTTP cookie. 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 retrieve the User object from the server-side session and refresh their session if it expires
- The browser requests the user's forum posts from the application backend and includes the session and refresh token cookies
- The application backend looks up the server-side session associated with the session cookie and extends the expiration date
- The application backend loads the User object (or JWT) from the session associated with the session cookie. The backend then 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 session id
- The application backend verifies the session id 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 receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
- 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 session id as a cookie that attacker can now use
- This is an attack vector where the attacker has stolen the user's session cookie. Here, the attacker requests the user's shopping cart with the stolen session cookie
- The application backend looks up the server-side session associated with the session cookie and extends the expiration date
- The application backend uses the session to look up the user's shopping cart. It responds to the attacker with the user's shopping cart HTML, CSS & JavaScript
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: