In this post we will talk about Authorisation Code with PKCE Flow(for browser, mobile & desktop apps). A variation of auth. code flow for clients which can’t protect a global secret. Better security than implicit grant / user-agent for similar use cases.
Additional requirements
- Browser – for user to authenticate and consent
- Client can generate and securely store a code_verifier
- Up to date security measures
What else to know
Proof key for code exchange supported by SHA256:
- Access token leakage risk reduced with HTTP POST
- POST request/response protects against access token injection
- More secure channel can be used for token request if available
- Security recommendations
| Vulnerability | Protection |
| PKCE downgrade | Auth server must enforce all requests for a given configuration to require code_challenge |
| CSRF | Use and verify state and nonce for request/response binding |
| Redirect to an attacker’s page | Client must not allow open redirects Auth server must not allow open redirects or pattern matching of redirect_uri |
Considerations for choosing authorisation code + PKCE
- Auth code request can be over relatively open channel
- Ideal for mobile, SPA, desktop apps etc where no secure client server involved
- Requires auth. server to support PKCE
Authorisation Code with PKCE Flow Video
