PKCEutvidelsen

PKCEutvidelsen refers to an extension or enhancement related to Public Key Cryptography, specifically within the context of authorization flows. It is a security mechanism designed to mitigate the authorization code interception attack in OAuth 2.0, particularly for public clients like mobile applications and single-page web applications. The acronym PKCE stands for Proof Key for Code Exchange.

The core idea behind PKCE is to dynamically create a secret for each authorization request. The client generates a random string, known as the `code_verifier`, and then creates a transformed version of this string, called the `code_challenge`, using a specific transformation method (typically SHA256). This `code_challenge` is sent to the authorization server along with the authorization request.

When the client receives the authorization code back from the server, it also sends the original `code_verifier` along with it during the token exchange process. The authorization server then independently transforms the received `code_verifier` using the same method it received the `code_challenge` with. If the transformed `code_verifier` matches the original `code_challenge`, the server knows that the client exchanging the code is the same client that initiated the authorization request, thus preventing an attacker from intercepting the authorization code and exchanging it for tokens. This adds a crucial layer of security for clients that cannot securely store a client secret.