Authorization Code with PKCE
Understand the security challenges faced by public OAuth 2.0 clients without client secrets and how PKCE enhances the authorization code flow. Discover how dynamically generated cryptographic verifiers and challenges prevent interception attacks and why PKCE is now mandatory for all OAuth clients, securing both mobile and backend applications.
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In the previous lesson, we established that public clients, such as mobile apps and single-page applications (SPAs), cannot safely store a client secret. Because their source code and binaries are accessible to the end user, any embedded secret is easily extracted. This creates a severe security gap during the standard authorization code token exchange. To bridge this gap, the OAuth 2.0 specification mandates the Proof Key for Code Exchange (PKCE) extension.
This lesson examines the specific vulnerability public clients face and demonstrates how PKCE uses dynamically generated cryptographic keys to secure the token exchange process.
Note: While PKCE was originally designed to protect public clients, the OAuth 2.1 specification now mandates PKCE for all clients, including confidential clients. This protects backend applications against a separate threat known as authorization code injection.
The vulnerability of public clients
Without a client secret, the authorization server has ...