Logo / Articles

Login & Auth Workflows

Single-Page Application OAuth Login Using Authorization Code Grant With Sessions - Recommended

By Brian Pontarelli

This workflow is used by single-page applications using the FusionAuth OAuth login interface. The single-page application navigates away from its interface and over to FusionAuth’s OAuth interface. Once the user completes their login, FusionAuth redirects back to the single-page application. This requires that the single-page application re-initialize itself, but the browser should cache the application files and be able to restart it quickly. 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
BrowserStoreForumsFusionAuthHackerInitializeLogin (browser navigates away from SPA)Shopping cart loadSession expiresRe-loginSSO login to forumsInitializeLogin (browser navigates away from SPA but auto-logs-in since the session exists)Forum loadAttack vectorsStolen session idGET /1(SPA HTML, CSS & JavaScript)2AJAX GET /api/user[No cookies]3404 Missing4GET /oauth2/authorize {response_type=code}5(Login form HTML)6POST /oauth2/authorize(response_type=code)7302 Location: {redirect_uri w/ code}[SessionId HttpOnly w/ domain: example.fusionauth.io]8GET {redirect_uri w/ code}9POST /oauth2/token(code, client_secret)10200 Ok(Refresh token and JWT - ignored)11Create session andstore User in it12302 Location: /[SessionId HttpOnly w/ domain: store.example.com]13GET /14(SPA HTML, CSS & JavaScript)15AJAX GET /api/user[SessionId HttpOnly w/ domain: store.example.com]16200 Ok(User)17AJAX GET /api/load-shopping-cart[SessionId HttpOnly w/ domain: store.example.com]18Session extended19(Shopping cart contents)20AJAX GET /api/load-shopping-cart[SessionId HttpOnly w/ domain: store.example.com]21401 Not Authorized22Login same as above23GET /[No cookies]24(SPA HTML, CSS & JavaScript)25GET /api/user[No cookies]26404 Missing27GET /oauth2/authorize {response_type=code}[SessionId HttpOnly w/ domain: example.fusionauth.io]28302 Location: {redirect_uri w/ code}[SessionId HttpOnly w/ domain: example.fusionauth.io]29GET {redirect_uri w/ code}30POST /oauth2/token(code, client_secret)31200 Ok(Refresh token and JWT - ignored)32Create session andstore User in it33302 Location: /[SessionId HttpOnly w/ domain: store.example.com]34GET /35(SPA HTML, CSS & JavaScript)36AJAX GET /api/user[SessionId HttpOnly w/ domain: store.example.com]37200 Ok(User)38AJAX GET /api/load-posts[SessionId HttpOnly w/ domain: forums.example.com]39Session extended40(Forum posts)41GET /api/load-shopping-cart[SessionId HttpOnly w/ domain: store.example.com]42Session extended43(Shopping cart contents)44BrowserStoreForumsFusionAuthHacker

Explanation

  1. The browser requests the shopping cart single-page application from the application backend
  2. The application backend responds with the HTML, CSS & JavaScript of the application
  3. The browser loads the application and as part of the initialization process, it makes a request to the application backend to see if the user is logged in
  4. The application backend responds with a 404 indicating the user is not logged in
  5. The user clicks the login link and the browser navigates away from the single-page application to FusionAuth's OAuth 2 interface. The browser requests the OAuth 2 login page from FusionAuth with a response_type of code indicating that it is using the authorization code grant
  6. FusionAuth responds with the HTML, CSS & JavaScript of the login page (including the form)
  7. The user inputs their credentials and clicks the submit button. The browser POSTs the form data to FusionAuth
  8. FusionAuth returns a redirect to the application backend's OAuth 2 redirect_uri. This redirect includes the authorization code from FusionAuth. Also, this response includes a session id for the FusionAuth OAuth 2 interface as an HTTP cookie. This cookie is HttpOnly, which prevents JavaScript from accessing it, making it less vulnerable to theft
  9. The browser requests the application backend's OAuth redirect_uri with the authorization code from FusionAuth
  10. The application backend calls FusionAuth's OAuth 2 token endpoint with the authorization code and optionally the client_secret
  11. FusionAuth verifies the authorization code and client_secret. It returns a 200 along with a JWT and refresh token in JSON
  12. The application backend receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
  13. The application backend returns a redirect back to the single-page application. The id of the server-side session is also written back to the browser in an HTTP cookie. This cookie is HttpOnly, which prevents JavaScript from accessing it, making it less vulnerable to theft. Additionally, all requests from the browser to the application backend will include this cookie so that the backend can retrieve the User object from the server-side session
  14. The browser requests the shopping cart single-page application from the application backend
  15. The application backend responds with the HTML, CSS & JavaScript of the application
  16. The browser loads the application and as part of the initialization process, it makes a request to the application backend to see if the user is logged in
  17. The application backend responds with a 200 and the User object (usually in JSON)
  18. The browser requests the user's shopping cart from the application backend via AJAX and includes the session cookie
  19. The application backend looks up the server-side session associated with the session cookie and extends the expiration date
  20. 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 shopping cart from the database (or similar location). Finally, the application backend returns the user's shopping cart (usually as JSON)
  21. A while later, the user's server-side session expires and the user clicks on their shopping cart again. The browser requests the shopping cart from the application backend via AJAX and sends the session cookie to the application backend
  22. The application backend attempts to load the server-side session associated with session cookie and realizes it is expired. The backend then returns a 401 indicating that the user is no longer logged in
  23. At this point, the application can allow the user to log in the same way they did above
  24. The browser requests the forum single-page application from the application backend. This is a standard SSO login that is fully supported by FusionAuth
  25. The application backend responds with the HTML, CSS & JavaScript of the application
  26. The browser loads the application and as part of the initialization process, it makes a request to the application backend to see if the user is logged in
  27. The application backend responds with a 404 indicating the user is not logged in
  28. The user clicks the login link and the browser navigates away from the single-page application to FusionAuth's OAuth 2 interface. The browser requests the OAuth 2 login page from FusionAuth with a response_type of code indicating that it is using the authorization code grant. Additionally, the session cookie that was set during the first login is also sent by the browser to FusionAuth
  29. FusionAuth realizes that the user already has a session and is already logged in. Therefore, it returns a redirect to the application backend's OAuth 2 redirect_uri. This redirect includes the authorization code from FusionAuth
  30. The browser requests the application backend's OAuth redirect_uri with the authorization code from FusionAuth
  31. The application backend calls FusionAuth's OAuth 2 token endpoint with the authorization code and optionally the client_secret
  32. FusionAuth verifies the authorization code and client_secret. It returns a 200 along with a JWT and refresh token in JSON. **NOTE**: all of this happens without any user interaction, hence the SSO nature of this login
  33. The application backend receives the 200 from FusionAuth and creates a server-side session and stores the User object (or JWT) in it
  34. The application backend returns a redirect back to the single-page application. The id of the server-side session is also written back to the browser in an HTTP cookie. This cookie is HttpOnly, which prevents JavaScript from accessing it, making it less vulnerable to theft. Additionally, all requests from the browser to the application backend will include this cookie so that the backend can retrieve the User object from the server-side session
  35. The browser requests the forums single-page application from the application backend
  36. The application backend responds with the HTML, CSS & JavaScript of the application
  37. The browser loads the application and as part of the initialization process, it makes a request to the application backend to see if the user is logged in
  38. The application backend responds with a 200 and the User object (usually in JSON)
  39. The browser requests the user's forum posts from the application backend via AJAX and includes the session cookie
  40. The application backend looks up the server-side session associated with the session cookie and extends the expiration date
  41. The application backend loads the User object (or JWT) from the session associated with the session cookie. 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 (usually as JSON)
  42. 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
  43. The application backend looks up the server-side session associated with the session cookie and extends the expiration date
  44. 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 contents (usually as JSON)

Security considerations

This a safe and feature rich login workflow in FusionAuth. It has the benefit that passwords are only provided directly to FusionAuth. It also has the benefit of full SSO capabilities when the user is automatically logged into the forum application by FusionAuth. The downside of this workflow is that the sessions might be shorter lived than refresh tokens, forcing the user to login more regularly. If this is the preferred behavior, than this workflow might be the best fit.

APIs used

Here are the FusionAuth APIs used in this example: