]> TaskHawk Systems LLC

Charlottesville VA United States of America j.mcgraw@taskhawktech.com

Web and Internet Transport HTTPAPI HTTP authentication status code budget delegated authority RateLimit COSE JOSE ML-DSA SLH-DSA CBOR Delegated software requesters are increasingly authorized to consume paid or metered services, allocate account credits, or commit bounded resources on behalf of human or organizational principals. Existing HTTP authentication mechanisms indicate whether a requester holds a credential, while RateLimit fields communicate server-advertised quota and current service-limit information. Neither mechanism directly conveys that the requester has been authorized by its principal to consume or commit resources within a bounded limit before a request is processed. This document defines the 427 (Budget Required) HTTP status code, the "Budget" HTTP authentication scheme, the Budget-Attestation HTTP field, and a CBOR/COSE Budget-Attestation envelope. The mechanism is algorithm-agile; the initial cose-ml-dsa profile uses existing JOSE and COSE serializations for ML-DSA, with ML-DSA-65 as the baseline algorithm and ML-DSA-87 available as a high-assurance deployment policy option. An optional rail-keyed SLH-DSA signature can be used by deployments that bind a budget attestation to a settlement rail. This document does not define payment semantics and does not depend on the HTTP 402 (Payment Required) status code. About This Document Status information for this document may be found at . Discussion of this document takes place on the HTTPAPI Working Group mailing list (), which is archived at . Subscribe at .

Introduction Delegated software requesters acting on behalf of human or organizational principals increasingly make HTTP requests that may incur cost, consume metered service units, or trigger settlement through an out-of-band rail. HTTP authentication addresses whether a requester holds a usable credential. RateLimit fields communicate server-defined quota policies and current service-limit information. Budget authorization addresses a distinct requirement: proving that the requester has been granted bounded authority by its principal to spend or consume a specified amount for a class of requests. This document defines:

• The 427 (Budget Required) HTTP status code (), used by an origin server or gateway to indicate that the request will not be processed until the requester presents a valid Budget-Attestation.
• The "Budget" HTTP authentication scheme (), used in the WWW-Authenticate response field of a 427 response and in the Authorization request field of a subsequent request.
• The Budget-Attestation HTTP field (), used when Budget authority is additive to another origin-server authentication mechanism already carried in Authorization.
• The Budget-Attestation envelope (), a CBOR-encoded , COSE-signed structure that carries semantic claims about issuer, requester, expiry, request binding, permitted rails, and amount.

The Budget status code and authentication scheme are algorithm-agile. The initial cose-ml-dsa profile uses ML-DSA algorithm identifiers serialized for JOSE and COSE by , using the ML-DSA algorithm specified in . Implementations of this profile MUST support ML-DSA-65 and MAY support ML-DSA-87. A deployment MAY require ML-DSA-87 or another registered algorithm by local policy. A deployment MAY add an optional rail-keyed signature using SLH-DSA, aligned with the JOSE and COSE SLH-DSA work in and the SLH-DSA algorithm specified in . That optional signature is not a replacement for the primary signature. This document does not define a payment protocol. Settlement rails such as L402 , x402 , card payments, or other systems can use Budget-Attestation as input to their own policy and settlement flows; however, their settlement semantics are outside the scope of this document. In particular, this document does not depend on, redefine, or reserve any semantics for HTTP 402 (Payment Required). Scope and modularization: Sections 3 and 4 define the HTTP status code, authentication challenge, credential syntax, and HTTP field semantics. Section 5 defines an initial COSE/CBOR Budget-Attestation profile to demonstrate an interoperable cryptographic binding for that HTTP mechanism. During standards progression, the Working Group can move the COSE/CBOR profile into a companion document for review by the COSE or OAuth communities without changing the core HTTP semantics defined by the status code, authentication scheme, and field carriage.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Operator:

An entity that issues Budget-Attestations on behalf of a principal.

Delegated Requester:

A client, workload, device, job, agent, or other software component that presents a Budget-Attestation issued by an Operator in order to make HTTP requests within delegated bounds.

Agent:

A delegated requester. The term "agent" remains the motivating deployment case and appears in existing claim names for wire compatibility; it is not a protocol requirement for any specific architecture.

Verifier:

An origin server, gateway, or intermediary that receives a Budget-Attestation, validates its signatures and claims, and decides whether to process the bearing request.

Budget-Attestation:

The CBOR-encoded, COSE-signed envelope defined in .

Settlement Rail:

An out-of-band protocol or payment system used to transfer value or record resource consumption. Rail names can appear as claims in a Budget-Attestation. This document does not define how any settlement rail operates.

Rail-Keyed Signature:

An optional additional signature over the Budget-Attestation envelope, intended to bind a deployment's rail-specific policy to the same claims that the primary Operator signature covers.

Applicability Budget is a general HTTP mechanism for delegated, bounded spend or resource authority. Autonomous software agents are the motivating deployment case; however, the mechanism also applies to service workloads, CI/CD jobs, IoT or fleet devices, batch systems, scheduled data processors, and other delegated requesters that need to prove bounded authority before a protected request is processed. The agent claim carries the delegated requester identifier. Deployments MAY populate it with an agent identifier, service-account identifier, workload identity, device identifier, job identifier, or privacy-preserving alias. The claim name is retained for compatibility with existing agent_id deployments and does not require the requester to be an AI system. A future revision MAY define a neutral alias for this claim; doing so needs a wire-compatibility plan so existing deterministic encodings and signed bytes are not broken unnecessarily.

Relationship to RateLimit Fields RateLimit fields describe service limits from the server to the client. They tell the client what quota policy applies and what capacity is currently available under that server-defined policy. They are useful for throttling, backoff, and avoiding 429 responses. Budget-Attestation travels in the opposite direction. It is a client-presented credential showing that an Operator authorized an Agent to spend or consume up to stated bounds. It is evaluated before the Verifier processes the protected request. This document defines a separate mechanism rather than extending RateLimit because a signed, bearer-presented authority object has different issuer, freshness, replay, and verification semantics from server-advertised quota metadata. Extending RateLimit-Policy would change the issuer and trust model of RateLimit from server-authored quota advertisement into principal-authored spending authorization, which is a different protocol semantic rather than a new quota parameter. The mechanisms are complementary:

• A server MAY return RateLimit fields on 200, 427, 429, or other responses when it wants to communicate server-side quota state.
• A server MUST NOT treat RateLimit fields as a substitute for Budget-Attestation, because RateLimit fields are not signed authority from the Agent's principal.
• A Budget-Attestation MUST NOT be interpreted as a server quota promise. It only states the Agent's delegated budget or resource authority.

Property	RateLimit fields	Budget-Attestation
Direction	Server to client	Client to verifier
Issuer	Resource server or gateway	Operator acting for the principal
Integrity	HTTP field semantics	COSE/JOSE signature
Purpose	Advertise quota and current service limits	Prove delegated spending or resource authority
Failure mode	Client might be throttled	Request fails before protected processing

Relationship to HTTP Message Signatures defines signatures over components of individual HTTP messages. Budget-Attestation signs a portable authority object whose claims can be evaluated independently of a single HTTP message. The two mechanisms can be composed: an Agent can send an HTTP-message signature that covers the request as transmitted and a Budget-Attestation that covers delegated budget authority.

Relationship to HTTP 402 HTTP 402 (Payment Required) is reserved by HTTP Semantics . Some deployed payment systems use 402 responses as part of their own settlement flows. This document neither depends on those deployments nor defines their semantics. An implementation MAY use Budget-Attestation before invoking a settlement rail. Whether that later settlement interaction uses HTTP 402, a 401 challenge, a signed request body, or another transport is out of scope for this document.

Overview of Operation A protected origin determines that a request requires budget authority and that no acceptable Budget credential is present: It returns: The Agent obtains a Budget-Attestation from its Operator by means outside this document and retries using body carriage: If the attestation is valid for the request and local policy, the Verifier processes the request normally. If validation fails, the Verifier returns 427 again and SHOULD include a reason extension member in the Problem Details body.

The 427 (Budget Required) Status Code The 427 (Budget Required) status code indicates that the requester must present a valid Budget-Attestation before the request can be processed. It differs from 401 (Unauthorized) because a requester can be authenticated and still lack budget authority. It differs from 429 (Too Many Requests) because 427 is not a statement about server-side quota exhaustion. It differs from 402 (Payment Required) because 427 asks for evidence of delegated spending or resource authority, not for immediate payment. A 427 response MUST include a WWW-Authenticate response field containing at least one Budget challenge. A 427 response SHOULD include Cache-Control: no-store as defined by HTTP caching . A 427 response that contains a nonce, requester-specific policy, or other policy-sensitive material MUST include Cache-Control: no-store. A 427 response SHOULD include an application/problem+json or application/problem+cbor body using . The 427 status code is distinct from existing alternatives. A 403 response is a general authorization refusal and does not define a machine-actionable challenge for acquiring a principal-signed delegation credential. A 402 response is payment-specific and would conflate Budget-Attestation with immediate settlement behavior that this document explicitly leaves out of scope. The 427 response defines a separate automated state transition: a delegated requester receives a Budget challenge, obtains a bounded authority object from its Operator, and retries without converting the exchange into a hard authorization denial or an in-band payment flow. Some deployment paths might contain intermediaries that do not pass an unrecognized 427 status code reliably. A deployment profile MAY use a 403 (Forbidden) response as a compatibility fallback only when the response carries the same Budget challenge information that a 427 response would have carried, including a WWW-Authenticate field with a Budget challenge and an application/problem+json or application/problem+cbor body containing a budget_requirements object. A client that implements this fallback MUST NOT treat arbitrary 403 responses as Budget challenges; it MAY treat a 403 response as equivalent to 427 only when the Budget challenge and Problem Details budget requirements are both present.

Budget Error Tokens When a Verifier returns a 427 response because a presented Budget credential failed validation, the Problem Details object SHOULD contain a reason extension member. The value of this member is a token identifying the validation failure. This document defines the following initial tokens:

• token_expired: The presented Budget-Attestation exp timestamp is in the past relative to the Verifier's clock.
• nonce_stale: The nonce in the attestation does not match a valid, unexpired challenge window.
• nonce_replay: The nonce has already been accepted by the Verifier within its replay-tracking window.
• bad_signature: Cryptographic validation of the primary signature or a required rail-keyed signature failed.
• untrusted_issuer: The iss claim identifies an issuer for which the Verifier has no explicit trust relationship.
• budget_insufficient: The authorized amt claim does not satisfy the budget requirement advertised by the resource server.
• version_unsupported: The version claim or Protocol-427-Version field is not supported by the Verifier.
• binding_mismatch: The request target URI, method, origin, or body digest does not match the signed rb object.

The "Budget" Authentication Scheme The Budget authentication scheme is used in WWW-Authenticate and Authorization fields.

Challenge Syntax The Budget authentication scheme challenge uses the auth-param syntax defined by , Section 11.2: The realm and nonce parameters are REQUIRED. The alg parameter identifies acceptable primary signature algorithms. The rails parameter identifies settlement rail names acceptable to the Verifier; rail semantics remain out of scope for this document. The nonce parameter MUST contain at least 128 bits of unpredictable entropy and MUST be generated by the Verifier for the protection space identified by realm. A Verifier MUST accept a nonce at most once. Replay of a nonce, absence of nonce state, or loss of the replay cache MUST cause the Verifier to reject the request. To reduce outstanding-challenge state, Verifiers SHOULD support self-authenticating nonce constructions. A self-authenticating nonce contains unpredictable bytes and integrity-protected metadata such as protection space, issuance time, key identifier, and policy binding. The nonce is authenticated with a server-held secret, for example using an HMAC or AEAD construction, and MUST NOT reveal that secret to clients. This construction allows a Verifier to validate the origin and age of a returned nonce without storing every issued challenge. It does not remove the requirement to enforce at-most-once acceptance; Verifiers still need accepted-nonce replay tracking or an equivalent replay-detection mechanism until the challenge can no longer be accepted. The max-age parameter, when present, is the validity window in seconds for the challenge parameters and nonce. It does not extend the Budget-Attestation lifetime. A Verifier MUST reject a Budget-Attestation whose nonce is older than max-age for the corresponding challenge. If max-age is omitted, Verifiers SHOULD apply a local default and that default SHOULD NOT exceed 900 seconds.

Credentials Syntax The credential token carries base64url-encoded COSE/CBOR. If the encoded envelope would exceed practical HTTP field size limits, the Agent MUST send the envelope in a request body with media type application/budget-attestation+cose. Implementations of the cose-ml-dsa profile MUST support request-body carriage. Requesters using that profile SHOULD use body carriage by default because ML-DSA-backed COSE envelopes are large before base64url expansion and can exceed field-size limits enforced by intermediaries. A deployment profile MAY permit field carriage with Authorization: Budget only when it defines accepted field-size limits and failure behavior. A Verifier MAY reject oversized field-carried credentials before CBOR or COSE decoding. A deployment MAY bind the body-carried envelope to the request using a digest claim in the envelope's request-binding structure.

Multi-Scheme Composition and the Budget-Attestation Field The Budget-Attestation field carries a Budget-Attestation when the request already uses Authorization for another origin-server credential or when a deployment wants Budget authority to be visibly additive to another authentication scheme. The field value is a Structured Field Item whose bare item is a Byte Sequence containing the COSE/CBOR Budget-Attestation envelope. If both Authorization: Budget and Budget-Attestation are present, the Verifier MUST reject the request unless a deployment profile explicitly defines how the two credentials compose. This avoids ambiguity about which signed authority object is authoritative. The Authorization field MUST NOT be used to concatenate a non-Budget credential and a Budget credential into a single field value unless a future HTTP authentication scheme explicitly defines such composition. When identity authentication uses Authorization, Budget authority SHOULD be carried in the request body for the cose-ml-dsa profile or, for bounded low-footprint deployments, in the Budget-Attestation field. When a request carries both an identity credential and a Budget-Attestation, the Verifier MUST evaluate the identity authentication layer and the budget delegation layer independently. Failure of the identity authentication layer is handled according to that authentication scheme, typically with 401 or 403. Failure of the budget delegation layer is handled with 427, or with the 403 compatibility fallback defined in . The Budget-Attestation field is not the general-purpose carriage path for multi-kilobyte post-quantum attestations. Implementations of the cose-ml-dsa profile MUST support body carriage with media type application/budget-attestation+cose. A deployment profile MAY permit Budget-Attestation field carriage only when it defines accepted field-size limits and failure behavior. If the target request also needs an unrelated representation body, that packaging profile MUST define how the Budget-Attestation and application representation are bound to each other.

The Budget-Attestation Envelope The Budget-Attestation envelope is a COSE object carrying a CBOR claims set. The claims set is encoded using deterministic CBOR . Encoders MUST follow the core deterministic encoding requirements of , Section 4.2.1. Verifiers MUST reject non-deterministic encodings and MUST verify signatures over the exact received deterministic encoding, not over a locally reserialized variant. This document defines the logical claims below using CDDL ; exact COSE encoding details can be profiled further during Working Group review. uint, "iss" => tstr, "agent" => tstr, "iat" => uint, "exp" => uint, "nonce" => bstr .size (16..64), "kid" => tstr, "rb" => Request-Binding, "rails" => [+ tstr], ? "cb" => Channel-Binding, ? "amt" => { + tstr => uint } } Request-Binding = { "method" => tstr, "uri-h" => bstr .size 32, "origin" => tstr, ? "body-h" => bstr .size 32 } Channel-Binding = { "type" => tstr, "value" => bstr } ]]> The amt claim carries the delegated amount bound inside the signed attestation. A 427 response can separately advertise min-budget in its Problem Details body; that response member is an input to client policy and does not become authoritative unless it is reflected in a signed amt claim. The CDDL above uses text claim names for readability in this early revision. A future revision can assign integer claim labels to reduce wire size without changing the semantics of the claims. The optional cb claim is reserved for binding an attestation to an external channel-binding value such as a TLS exporter. This document defines the claim container but does not define mandatory channel-binding types. A Verifier MUST reject a cb claim whose type it does not understand or whose value does not match the locally computed channel-binding value for that type.

Primary Signature Every Budget-Attestation MUST contain exactly one primary Operator signature. The primary signature MUST use an ML-DSA algorithm identifier registered for JOSE or COSE by . The Budget status code and authentication scheme are algorithm-agile. The cose-ml-dsa profile defined by this document has the following interoperability requirements:

• Implementations of this profile MUST support ML-DSA-65.
• Implementations MAY support ML-DSA-87.
• Deployments MAY require ML-DSA-87 or another registered algorithm by local policy.
• Verifiers MUST validate that the signed protected-header algorithm matches local policy and MUST reject algorithm downgrades.

Future documents can define additional Budget-Attestation profiles using other COSE or JOSE algorithm identifiers without changing the semantics of the 427 status code or the Budget authentication scheme.

Operator Key Discovery and Trust A Verifier MUST establish trust in an Operator public key before accepting a Budget-Attestation signed by that key. Trust can be established through local configuration, an authenticated out-of-band agreement, or an issuer-controlled HTTPS key-set endpoint. A Verifier MUST NOT treat an untrusted iss value or arbitrary key URL in an attestation as sufficient authority to trust a key. One interoperable deployment profile is an issuer-controlled HTTPS key-set URI, for example https://example.com/.well-known/budget-issuer-keys, returning a COSE_KeySet with media type application/cose-key-set. A Verifier using this profile MUST authenticate the HTTPS origin, MUST require each accepted key to carry a key identifier usable as kid, MUST bind each key to the expected issuer and algorithm policy, and MUST reject the request if the key set is unavailable or omits the referenced key. Cached key material MUST NOT be used beyond its authenticated freshness lifetime. Key rotation SHOULD provide overlap between old and new keys for already-issued attestations.

Optional Rail-Keyed Signature A Budget-Attestation MAY contain an additional rail-keyed signature. A rail-keyed signature MUST NOT replace the primary Operator signature and MUST NOT be accepted when the primary signature fails. When a deployment uses SLH-DSA for rail-keyed signatures, it SHOULD use the JOSE or COSE serializations defined by once those registrations are available. Until then, private-use algorithm identifiers MUST be treated as deployment-specific and MUST NOT be advertised as interoperable. Because SLH-DSA signatures can be tens of kilobytes, an attestation that contains a rail-keyed SLH-DSA signature MUST be carried in a request body using application/budget-attestation+cose rather than in an HTTP field.

Verification A Verifier processing a Budget-Attestation MUST:

1. Decode the CBOR envelope and reject non-deterministic or malformed encodings.
2. Verify that the version is supported.
3. Verify the primary signature against an Operator key authorized for the issuer and kid.
4. Verify iat, exp, clock skew, and maximum lifetime. Verifiers MUST reject attestations where exp - iat exceeds 900 seconds and SHOULD apply no more than 60 seconds of clock-skew tolerance unless local policy is stricter. Operators and Verifiers SHOULD synchronize clocks using an authenticated time source suitable for the deployment.
5. Verify that nonce matches a live challenge and has not been used before.
6. Verify request binding against the bearing request, including method, origin, target URI hash, and body hash when present.
7. Verify rail policy if a rails claim is present.
8. Verify any rail-keyed signature required by local policy.

Failure at any step MUST cause the Verifier to reject the request.

Versioning This document defines version 1 of the Budget authentication scheme and Budget-Attestation envelope. A 427 response MUST include a Protocol-427-Version response field containing a Structured Field Integer . A client that receives an unknown Protocol-427-Version value MUST NOT guess at wire compatibility. It MAY retry using a version it supports only when the server advertises that version through local policy or a future version-negotiation mechanism. A server that receives a Budget credential or Protocol-427-Version request value for an unsupported version MUST reject the request with 427 and a version_unsupported reason code, unless a future revision defines a different upgrade response.

IANA Considerations This section follows the guidance in and . The requested registrations use the existing HTTP and media-type registries.

HTTP Status Code IANA is asked to register the following entry in the "Hypertext Transfer Protocol (HTTP) Status Code Registry" defined by :

Status Code	Short Description	Reference
427	Budget Required	This document,

HTTP Authentication Scheme IANA is asked to register the following entry in the "Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry" defined by :

Authentication Scheme Name	Reference	Notes
Budget	This document,	Origin-server authentication using WWW-Authenticate and Authorization; not defined for proxy authentication

HTTP Field Name IANA is asked to register the following entry in the "Hypertext Transfer Protocol (HTTP) Field Name Registry":

Field Name	Status	Structured Type	Reference	Comments
Protocol-427-Version	permanent	Integer	This document,	Version of the Budget authentication scheme and Budget-Attestation envelope
Budget-Attestation	permanent	Byte Sequence	This document,	Additive carriage of a Budget-Attestation when Authorization is used by another origin-server scheme

Budget Error Token Registry IANA is asked to create a "Budget Error Tokens" registry for tokens used in the Problem Details reason extension member defined by . The registration policy is Specification Required . Initial registrations are:

Token	Description	Reference
token_expired	The attestation expired.
nonce_stale	The nonce is outside the accepted challenge window.
nonce_replay	The nonce was already accepted in the replay-tracking window.
bad_signature	A required signature failed validation.
untrusted_issuer	The issuer is not trusted by the Verifier.
budget_insufficient	The signed budget bounds do not satisfy the resource requirement.
version_unsupported	The protocol or attestation version is unsupported.
binding_mismatch	The signed request binding does not match the bearing request.

Media Type IANA is asked to register the following media type in the "Media Types" registry using the template from :

Type name:

application

Subtype name:

budget-attestation+cose

Required parameters:

N/A

Optional parameters:

cose-type, with the same semantics as the cose-type parameter for application/cose in .

Encoding considerations:

binary

Security considerations:

See .

Interoperability considerations:

Implementations need to support COSE processing, deterministic CBOR, and the algorithm identifiers profiled by this document.

Published specification:

This document.

Applications that use this media type:

HTTP clients, gateways, and origin servers that exchange Budget-Attestation envelopes.

Fragment identifier considerations:

This media type does not support fragment identifiers.

Additional information:

Deprecated alias names for this type: N/A; Magic number(s): N/A; File extension(s): N/A; Macintosh file type code(s): N/A.

Person & email address to contact for further information:

John McGraw, j.mcgraw@taskhawktech.com

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

John McGraw

Change controller:

IESG

Provisional registration?

No

Security Considerations Budget-Attestation is a bearer credential until verified. HTTP exchanges carrying it MUST use TLS. Servers SHOULD scrub Authorization field values, Budget-Attestation field values, and body-carried Budget credential values from logs. Verifiers MUST validate every check in before processing the protected request. Missing keys, unavailable verification dependencies, malformed CBOR, non-deterministic CBOR, expired attestations, signature failures, nonce replay, unsupported versions, and loss of nonce state all require request rejection. The COSE or JOSE algorithm identifier is part of the signed protected metadata. Verifiers MUST compare it against configured policy and MUST NOT let a challenge parameter or client preference downgrade the algorithm. Rail-keyed signatures are additive. They do not create authority without a valid primary Operator signature. Key lifecycle is security-critical. Operators SHOULD rotate signing keys on a predictable schedule, publish revocation information through the same trust channel used for key distribution, and avoid issuing attestations whose lifetime extends beyond the authenticated lifetime of the signing key. Verifiers MUST reject attestations signed by revoked, expired, or unexpected keys. Large post-quantum signatures can create denial-of-service pressure on HTTP parsers, HTTP field-section processing, and COSE libraries. ML-DSA-backed COSE envelopes are commonly too large to assume safe carriage through general-purpose HTTP fields after base64url expansion. Implementations MUST apply size limits before decoding, MUST bound CBOR nesting depth and map sizes, and SHOULD reject duplicate or unknown critical protected parameters before expensive signature verification. Verifier nonce state can itself become a resource-exhaustion target. Verifiers MUST bound the number of outstanding nonces per issuer, protection space, and client identity signal available to the deployment, and MUST expire unused nonces no later than their challenge max-age. When nonce state reaches a configured limit, the Verifier MUST reject requests that depend on an untracked nonce or shed unauthenticated challenge issuance rather than accept a request with an untracked nonce. At high scale, deployments SHOULD use self-authenticating nonces as described in so challenge issuance does not require allocating distributed state for every unauthenticated request. Such constructions reduce outstanding-challenge state but do not remove the need for bounded accepted-nonce replay tracking when at-most-once acceptance is required. This version defines an optional cb claim container for deployments that need binding to a particular TLS session or exporter value. Specific channel-binding types are not mandatory-to-implement in this revision and need profiling before they can be assumed interoperable. In the absence of channel binding, short lifetimes, single-use nonces, request binding, and replay-cache enforcement are mandatory replay controls.

Privacy Considerations These considerations are informed by the privacy guidance in . Budget-Attestations can reveal delegated requester identifiers, issuer identifiers, rail preferences, and amount limits. Implementations SHOULD use short lifetimes, random nonces, data minimization in requester identifiers, and body carriage when field logging by intermediaries would create avoidable privacy risk.

References

References Normative References Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234. Applications often use HTTP as a substrate to create HTTP-based APIs. This document specifies best practices for writing specifications that use HTTP to define new application protocols. It is written primarily to guide IETF efforts to define application protocols using HTTP for deployment on the Internet but might be applicable in other situations. This document obsoletes RFC 3205. This document defines a "problem detail" to carry machine-readable details of errors in HTTP response content to avoid the need to define new error response formats for HTTP APIs. This document obsoletes RFC 7807. This document describes a set of data types and associated algorithms that are intended to make it easier and safer to define and handle HTTP header and trailer fields, known as "Structured Fields", "Structured Headers", or "Structured Trailers". It is intended for use by specifications of new HTTP fields. This document obsoletes RFC 8941. This document specifies JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE) serializations for the Module-Lattice-Based Digital Signature Standard (ML-DSA), a Post-Quantum Cryptography (PQC) digital signature scheme defined in US NIST FIPS 204. National Institute of Standards and Technology (NIST) In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References This document offers guidance for developing privacy considerations for inclusion in protocol specifications. It aims to make designers, implementers, and users of Internet protocols aware of privacy-related design choices. It suggests that whether any individual RFC warrants a specific privacy considerations section will depend on the document's content. This document describes a simple process that allows authors of Internet-Drafts to record the status of known implementations by including an Implementation Status section. This will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. This process is not mandatory. Authors of Internet-Drafts are encouraged to consider using the process for their documents, and working groups are invited to think about applying the process to all of their protocol specifications. This document obsoletes RFC 6982, advancing it to a Best Current Practice. This document describes a mechanism for creating, encoding, and verifying digital signatures or message authentication codes over components of an HTTP message. This mechanism supports use cases where the full HTTP message may not be known to the signer and where the message may be transformed (e.g., by intermediaries) before reaching the verifier. This document also describes a means for requesting that a signature be applied to a subsequent HTTP message in an ongoing HTTP exchange. Team Digitale, Italian Government Red Hat Microsoft This document defines the RateLimit-Policy and RateLimit HTTP header fields for servers to advertise their quota policies and the current service limits, thereby allowing clients to avoid being throttled. mesur.io Tradeverifyd University of the Bundeswehr Munich This document specifies JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE) serializations for Stateless Hash-Based Digital Signature Standard (SLH-DSA), a Post- Quantum Cryptography (PQC) digital signature scheme defined in US NIST FIPS 205. National Institute of Standards and Technology (NIST) Coinbase, Inc. Lightning Labs

Implementation Status This appendix follows and is to be removed before publication as an RFC.

Kevros TaskHawk Systems operates a Kevros implementation that emits 427 challenges, publishes discovery and health metadata for deployment profiles, and records reason-coded audit events. Private no-spend proof workflows exist for Budget-Attestation verification, but each run is evidence only for the specific commit and deployment state under test. Challenge emission, Budget-Attestation verification, rail observation, settlement, and revenue are separate evidence lanes and are not equivalent. This implementation is provided as implementation experience only; it is not required for interoperability.

Changes Since -00

• Removed language implying HTTP 402 semantics are controlled by deployed payment protocols.
• Added and .
• Updated ML-DSA serialization references to and changed the initial cose-ml-dsa interoperability baseline to ML-DSA-65, with ML-DSA-87 available as a high-assurance deployment policy option.
• Kept rail-keyed SLH-DSA optional and body-carried.
• Made body carriage mandatory to implement for the cose-ml-dsa profile and recommended by default for post-quantum Budget-Attestation envelopes.
• Kept Authorization: Budget and Budget-Attestation as explicitly bounded field-carriage options for deployment profiles that define accepted field sizes and failure behavior.
• Added nonce replay, key-distribution, IANA, deterministic-CBOR, and expanded security text based on review feedback.
• Aligned the attestation lifetime rule with implementation behavior: exp - iat greater than 900 seconds is a verifier rejection condition.
• Tightened Implementation Status to separate challenge emission, Budget-Attestation verification, rail observation, settlement, and revenue.