The Proof Key for Code Exchange (PKCE) is a security extension to the OAuth 2.0 authorization framework. It is designed to prevent certain types of attacks, such as code interception and replay attacks, by providing an additional layer of verification.
The PKCE works as follows:
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The client initiates the authorization request with the authorization server. Instead of providing a client secret, the client creates a random string called the "code verifier" and generates a "code challenge" from it.
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The authorization server responds with an authorization code and includes the code challenge in the response.
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The client retrieves the authorization code and constructs a "code verifier".
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The client sends the authorization code along with the code verifier to the authorization server to obtain an access token.
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The authorization server validates the authorization code and verifies the code verifier against the original code challenge. If they match, the server issues an access token to the client.
The main benefit of PKCE is that it adds an extra layer of security during the authorization code exchange process. It ensures that even if an attacker intercepts the authorization code, they cannot exchange it for an access token without the original code verifier.
PKCE is especially useful in mobile and native applications, where secure storage of a client secret is challenging. It prevents attackers from extracting the client secret from the application and using it to gain unauthorized access.
In summary, the PKCE provides a proof mechanism during the authorization code exchange process, enhancing the security of OAuth 2.0. It helps protect against code interception and replay attacks, particularly in mobile and native applications.