Web Bot Auth explained: cryptographically verifying AI agents (RFC 9421)
Every detection method up to this point is inference: a UA string, an IP range, a fingerprint, a guess. Web Bot Auth is the one piece of the stack that is not a guess.
In short
Web Bot Auth has a bot sign each HTTP request with an Ed25519 private key, using the HTTP Message Signatures standard (RFC 9421); your server checks the signature against a public key the bot operator publishes at a well-known URL. A valid signature is cryptographic proof of identity, not a spoofable claim. Cloudflare shipped support 1 July 2025 and AWS WAF followed in November 2025, with Amazon, Akamai, and OpenAI named as backers - but the specification itself is still an individual IETF Internet-Draft, not a ratified standard, as of August 2026.
Landscape as of September 2026
The mechanism, plainly
Web Bot Auth applies RFC 9421 (HTTP Message Signatures, a ratified IETF standard for signing HTTP requests) to the specific problem of bot identity. A bot operator generates an Ed25519 keypair, publishes the public key at a well-known URL under its own domain, and signs each outgoing request with the private key. Your server, on receiving the request, fetches the operator's public key and verifies the signature against it. If it checks out, you know cryptographically which key signed the request - and, by extension, which operator's infrastructure it came from - without trusting anything the client merely claims about itself.
This inverts the usual bot-detection posture. Every other signal in how to detect AI agent traffic - user-agent, IP range, TLS fingerprint, timing - is something the server infers about the client. A signature is something the client proves to the server. That is a structurally different kind of evidence, which is why it ranks above everything else in the signal stack.
Where it stands
Milestone
Date
Detail
Cloudflare Verified Bots on signatures
1 Jul 2025
Cloudflare shipped cryptographic bot verification built on this signing scheme, the first major production deployment
AWS WAF support
Nov 2025
AWS added support for verifying signed bot requests in its WAF product
Named backers
ongoing
Amazon, Akamai, and OpenAI are named publicly as supporters of the approach
Standardization status
as of Aug 2026
Still an individual Internet-Draft at the IETF - not a working-group document, not an approved RFC. RFC 9421 (the underlying signature mechanism) is ratified; the bot-identity application of it is not yet standardized.
What it does not fix by itself
A signature only exists where the bot operator chose to sign. Most acting agents today do not - the directory in AI agent user-agents shows several major agents shipping no distinguishing signal at all, let alone a cryptographic one. And a missing signature proves nothing either way: it could mean an unsigned legitimate agent, or a spoofed request pretending to be one. Web Bot Auth strengthens the top of the signal stack; it does not replace the rest of it, which is why the block-or-measure decision still has to account for agents this specification does not yet cover.
Common questions
Is Web Bot Auth an official internet standard?
Not yet. As of August 2026 it is still an individual Internet-Draft at the IETF, not a working-group document or an approved RFC. RFC 9421 itself (HTTP Message Signatures, the signing mechanism it builds on) is a ratified standard; Web Bot Auth is the proposed application of it to bot identity, and that application is still pre-standardization.
How is this different from just checking the user-agent string?
A user-agent string is a claim - any client can type it. A Web Bot Auth signature is a cryptographic proof: the request is signed with a private Ed25519 key, and your server checks it against the public key the bot operator publishes at a well-known URL. A signature can be forged only by someone holding the private key, which is the entire point.
Who has actually shipped support for this?
Cloudflare shipped Verified Bots support built on this signing scheme on 1 July 2025. AWS WAF added support in November 2025. Backers named publicly include Amazon, Akamai, and OpenAI. Adoption is real but concentrated in a handful of infrastructure vendors and a subset of bot operators, not yet universal.
Does Web Bot Auth solve agent detection by itself?
It solves the hardest part of one signal - proving an identity claim - not the whole classification problem. An unsigned request from a legitimate agent still needs the composite signals covered in how to detect AI agent traffic. Treat a verified signature as the strongest evidence you can get, and everything else as the fallback for when it is absent.
Verify signed agents where you can. Classify the rest properly.
We build the request-level verification and the composite fallback together, so the pipeline doesn't silently drop everything a signature doesn't cover.