lion-screen-before-pay

lion-screen-before-pay

x402 verifies the payment, never who you are paying. An agent will happily send USDC to a payTo that belongs to a sanctioned, fraudulent, or honeypot counterparty. Screen first, pay second.

When to use

Whenever the agent is about to pay an x402 resource — or onboard/transact with any wallet, domain, or company. Screen the payTo before signing the payment.

The gate (one keyless call, $0.001 USDC on Base)

GET https://lionx402.com/api/x402/wallet-screen-json?address=<PAYTO>

• address = the wallet you are about to pay.
• Response: { "verdict": "PASS" | "WARN" | "BLOCK", "ofac": { "snapshot_as_of", "total_listed_addresses" }, "attestation" }.
• Proceed on PASS. Abort on WARN or BLOCK. Do not look for CLEAR.
• The $0.05 compliance bundle is optional, and only when this screen is not enough: GET https://lionx402.com/api/x402/compliance-bundle-json?address=<PAYTO>&receipt=1.

Workflow

1. Hit the target resource without paying. On 402, read payTo from the PAYMENT-REQUIRED header (base64 JSON, accepts[0].payTo). Use the JSON body only if that header is absent. LION's own 402 body is {}.
2. Screen it — pay the $0.001 wallet screen for that payTo (it is itself an x402 call; pay it with the cdp-x402 buyer flow below).
3. Decide: verdict == "PASS" → proceed to pay the target. WARN or BLOCK → ABORT.
4. Keep the signed body. It verifies offline (no callback) against LION's published key.

Screening the gate (reuses the cdp-x402 buyer flow)

PAYTO=0x...                      # the counterparty you're about to pay
LION="https://lionx402.com/api/x402/wallet-screen-json?address=$PAYTO"

REQ=$(curl -s "$LION" | jq -c '.accepts[0]')                 # LION 402 challenge
addr=$(cdp evm accounts by-name name=$ACCOUNT | jq -r .address)
payload=$(cdp util x402 build --from $addr --payment-requirements "$REQ")
D=$(echo "$payload" | jq -c .domain); T=$(echo "$payload" | jq -c .types)
P=$(echo "$payload" | jq -r .primaryType); M=$(echo "$payload" | jq -c .message)
sig=$(cdp evm accounts sign typed-data $addr \
  "domain:=$D" "types:=$T" "primaryType=$P" "message:=$M" | jq -r .signature)
header=$(cdp util x402 encode --payment-requirements "$REQ" \
  --signature "$sig" --authorization "$M" --x402-version 2)

RESULT=$(curl -s -H "X-PAYMENT: $header" -H "PAYMENT-SIGNATURE: $header" "$LION")
verdict=$(echo "$RESULT" | jq -r '.verdict // .receipt.verdict')
if [ "$verdict" != "PASS" ]; then
  echo "BLOCKED ($verdict): $(echo "$RESULT" | jq -c '.flags')"; exit 1   # fail-closed: do NOT pay
fi
echo "$RESULT" | jq -c '.' > last_wallet_screen.json                       # keep the proof
# verdict PASS -> now pay the original target resource.