Extensions

Sign In With X

Recognize returning wallets so repeat customers can skip paying again when your policy allows it—without replacing normal x402 payment verification.

Why use it

  • Wallet-based sign-in tied to the same flow agents already use for payments.
  • Server and client only; the facilitator does not participate in the authentication handshake.
  • Identity and payment policy stay separate: a product can reuse the session while still charging every request.

How it works

  • Your server advertises Sign In With X support on payment required responses.
  • The client proves control of an address with a signed challenge; your app decides when to waive or reduce charges.

Highlighting Request

  1. Request

    Wallet, agent, or app that selects an offer and signs payment.

    GET
    GET

    Sells access and publishes payment requirements.

    GET

    Verifies signatures and submits chain transactions on behalf of merchants.

  2. 402

    Your server advertises Sign In With X support on payment required responses.

    Wallet, agent, or app that selects an offer and signs payment.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    { "x402Version": 2 }

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Sells access and publishes payment requirements.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Verifies signatures and submits chain transactions on behalf of merchants.

  3. Pay and retry

    Wallet, agent, or app that selects an offer and signs payment.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Sells access and publishes payment requirements.

    Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

    Verifies signatures and submits chain transactions on behalf of merchants.

  4. Verify

    Wallet, agent, or app that selects an offer and signs payment.

    Sells access and publishes payment requirements.

    verify
    verify

    Verifies signatures and submits chain transactions on behalf of merchants.

    verify

  5. Settle

    Wallet, agent, or app that selects an offer and signs payment.

    Sells access and publishes payment requirements.

    settle
    settle

    Verifies signatures and submits chain transactions on behalf of merchants.

    settle

  6. Response

    Wallet, agent, or app that selects an offer and signs payment.

    200
    200

    Sells access and publishes payment requirements.

    200

    Verifies signatures and submits chain transactions on behalf of merchants.

Learn more

Read the extension spec (opens in a new tab)Extension docs (opens in a new tab)
For engineers

Extension key sign-in-with-x.

Server ↔ client extension per CAIP-122; facilitator is out of scope for SIWX.

  • Extension key sign-in-with-x on PaymentRequired extensions.
  • Challenge/response semantics and payload fields are defined in the extension spec.
  • Complements scheme verification; does not replace it.