PKCEä

PKCE stands for Proof Key for Code Exchange. It is an extension to the OAuth 2.0 authorization code grant flow designed to mitigate the security risk of authorization code interception. This attack vector is particularly relevant for public clients, such as native mobile applications and single-page web applications, which cannot securely store client secrets.

The PKCE flow involves the client generating a random string called the "code verifier". This code verifier is then transformed into a "code challenge" using a cryptographic hash function, typically SHA-256. The code challenge is sent to the authorization server along with the authorization request. The authorization server stores the code challenge and returns it to the client along with the authorization code.

When the client exchanges the authorization code for an access token, it must also send the original code verifier. The authorization server then re-calculates the code challenge from the provided code verifier and compares it to the stored code challenge. If they match, the authorization server issues the access token, confirming that the client requesting the token is the same client that initiated the authorization request. If they do not match, the token request is rejected, preventing an attacker who might have intercepted the authorization code from obtaining an access token. PKCE significantly enhances the security of OAuth 2.0 for public clients by ensuring that only the legitimate client can complete the token exchange process.