3.2.10. Proof Key for Code Exchange (PKCE)

Proof Key for Code Exchange (PKCE) minimizes the risk of authorization code interception.

While PKCE is of primary importance to public OIDC clients, such as SPA scripts running in a browser, it can also provide extra protection to Quarkus OIDC web-app applications. With PKCE, Quarkus OIDC web-app applications act as confidential OIDC clients that can securely store the client secret and use it to exchange the code for the tokens.

You can enable PKCE for your OIDC web-app endpoint with a quarkus.oidc.authentication.pkce-required property and a 32-character secret that is required to encrypt the PKCE code verifier in the state cookie, as shown in the following example:

quarkus.oidc.authentication.pkce-required=true
quarkus.oidc.authentication.state-secret=eUk1p7UB3nFiXZGUXi0uph1Y9p34YhBU

If you already have a 32-character client secret, you do not need to set the quarkus.oidc.authentication.pkce-secret property unless you prefer to use a different secret key. This secret will be auto-generated if it is not configured and if the fallback to the client secret is not possible in cases where the client secret is less than 16 characters long.

The secret key is required to encrypt a randomly generated PKCE code_verifier while the user is redirected with the code_challenge query parameter to an OIDC provider to authenticate. The code_verifier is decrypted when the user is redirected back to Quarkus and sent to the token endpoint alongside the code, client secret, and other parameters to complete the code exchange. The provider will fail the code exchange if a SHA256 digest of the code_verifier does not match the code_challenge that was provided during the authentication request.