Web Bot Auth vs Visa TAP: How to Verify AI Agents

Developer Tom Wang tested the signed-request examples in Visa's Trusted Agent Protocol and Mastercard's Agent Pay specs and found both fail Ed25519 verification, because each reuses an IETF test-vector signature over a different message and sets a 60-minute validity window that exceeds the 8-minute limit both networks tell merchants to enforce. His guide compares the three agent-identity schemes — Web Bot Auth, Visa TAP and Mastercard Agent Pay — all built on RFC 9421 HTTP Message Signatures, and shows verification code that handles their differing tags, windows, nonces and header syntax. Web Bot Auth remains an IETF draft, with the webbotauth working group chartered on 23 October 2025 and its only adopted document published 1 September 2026, even as Cloudflare, Akamai, AWS WAF, Vercel and HUMAN already verify signatures.

Copy the signed request from Visa's Trusted Agent Protocol spec into a unit test, run it through an Ed25519 verifier, and it fails. Mastercard's Agent Pay example fails too. Both reuse a signature from an IETF test vector that signs a different message, and both set a 60-minute validity window that breaks the 8-minute limit each network tells merchants to enforce. Web Bot Auth, Visa TAP and Mastercard Agent Pay are how an AI agent proves who it is to a merchant's website in 2026. All three sit on RFC 9421 HTTP Message Signatures, and they disagree on tags, windows, nonces and the syntax of a single header. This guide shows a real signed request, the signature base a verifier rebuilds, and verification code that copes with all three. Web Bot Auth gives bots and AI agents a cryptographic identity at the HTTP layer. The agent operator signs each request with a private key and publishes the public key in a directory. The site verifies the signature and knows which operator sent it, with no shared secret and no change to TLS. It is still a draft. The IETF chartered the webbotauth working group on 23 October 2025, and its only adopted document is draft-ietf-webbotauth-httpsig-protocol-00 , published 1 September 2026 by authors from Cloudflare and Google. Adoption was contested: the poll at IETF 126 came out 22 yes, 6 no, 5 no opinion. Deployment has run ahead of the standard anyway. Cloudflare, Akamai, AWS WAF, Vercel and HUMAN verify signatures; ChatGPT's cloud browser, Google-Agent and AWS AgentCore Browser send them. On 23 October 2026 IANA registered ml-dsa-44 , ml-dsa-65 and ml-dsa-87 for HTTP Message Signatures, though Cloudflare and AWS WAF still accept Ed25519 only. These headers are the current draft's own example Appendix E.2.1 , with line wrapping removed: Signature-Agent: agent2="https://signature-agent.test" Signature-Input: sig2= "@authority" "signature-agent";key="agent2" ;created=1735689600;keyid="poqkLGiymh W0uP6PZFw-dvez3QJT5SolqXBCW38r0U";alg="ed25519";expires=4889289600;nonce="n9p433xm+NJ3ph3upfBIGmsuwHw387YV7Q/F+6BSpGCVjYCqQw6rznNA8PVVLySrAWsv0hQtFioQb6E1YsauiA==";tag="web-bot-auth" Signature: sig2=:RdNFx5Bj6au3YgAMQL/RzmUlZE8QZLIaXGRpw985hWnwPfMxT228NMk6ehRS1PSl4e8PhbNZACSanGdhEwYCCg==: The verifier does not check the headers directly. It rebuilds a signature base , one line per covered component, with @signature-params required as the last line: "@authority": example.com "signature-agent";key="agent2": "https://signature-agent.test" "@signature-params": "@authority" "signature-agent";key="agent2" ;created=1735689600;keyid="poqkLGiymh W0uP6PZFw-dvez3QJT5SolqXBCW38r0U";alg="ed25519";expires=4889289600;nonce="n9p433xm+NJ3ph3upfBIGmsuwHw387YV7Q/F+6BSpGCVjYCqQw6rznNA8PVVLySrAWsv0hQtFioQb6E1YsauiA==";tag="web-bot-auth" Those bytes verify against the RFC 9421 Appendix B.1.4 Ed25519 test key. I checked. The key is public, so the vector is for tests only. What the draft requires of a signer: @authority or @target-uri , plus the Signature-Agent member that belongs to this signature. created , expires , a keyid that "MUST be a base64url JWK SHA-256 Thumbprint", and tag set to web-bot-auth . /.well-known/http-message-signatures-directory , media type application/http-message-signatures-directory+json , HTTPS only. Failed lookups may be cached for at most five minutes. There is no revocation. Read the full article on tomcn.uk → https://tomcn.uk/news/2026-10-26-web-bot-auth-vs-visa-tap-mastercard-agent-pay I'm Tom Wang , an AI Developer & Fintech Developer — building AI agents, crypto payment infrastructure, and cross-border payout systems with Rust, Go, and TypeScript. Based in London, UK. Currently open to new opportunities in fintech, crypto payments, and AI agent engineering.