X402 Extensions

This crate provides concrete extension type implementations for the X402 protocol.

Extensions enable modular optional functionality beyond core payment mechanics. Servers advertise supported extensions in PaymentRequired, and clients echo them in PaymentPayload.

Available Extensions

• [bazaar]: Resource discovery and cataloging for x402-enabled endpoints and MCP tools
• [sign_in_with_x]: Authenticated sign-in alongside payment

Defining Custom Extensions

You can define your own extensions by implementing the ExtensionInfo trait from x402-core:

use serde::{Serialize, Deserialize};
use x402_core::types::{Extension, ExtensionInfo, AnyJson};
use serde_json::json;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MyExtensionInfo {
    pub custom_field: String,
}

impl ExtensionInfo for MyExtensionInfo {
    const ID: &'static str = "my-custom-extension";
    fn schema() -> AnyJson {
        json!({
            "type": "object",
            "properties": {
                "custom_field": { "type": "string" }
            },
            "required": ["custom_field"]
        })
    }
}

let ext = Extension::typed(MyExtensionInfo {
    custom_field: "hello".to_string(),
});
let (key, transport) = ext.into_pair();
assert_eq!(key, "my-custom-extension");